How to test an Alternator (not charging from a blown fuse) - Mazda

Part 2 (why did the fuse blow) • How to find a short to...
This video covers the basic procedures needed to check an alternator that’s not charging, as well as some in-depth insight into the field control circuits. The bulb circuit bypass test shown is particularly valuable to learn, and applies to many other alternator designs, not just Mazda. Be sure to check out Part 2 for the follow up to this video, and some lessons on short to ground testing!
Engine Performance Diagnostics chapter 1
Symptoms
- dead battery
- inoperative dash lights/gauges
- stall
- engine won’t crank
Fix
- replace the blown fuse (short found in Part 2)
Tests shown
- using a wiring diagram to dissect an alternator control system
- how to check for charging voltage at the alternator
- using voltage drop to check the alternator B+ circuit
- understanding how a discharging battery can skew your readings
- checking the field control circuits, including the bulb circuit
- how to perform a bypass test with an incandescent test light
- using the key on bulb check to identify a bulb problem
- how to check fuses with a test light
- using voltage drop to check the alternator ground
- understanding how the alternator regulator controls the cluster bulb
- incandescent vs. LED test lights
Tools used
- ATD Tools 5519 Auto Ranging Digital Multimeter with Protective Holster
www.jbtoolsale...
- OTC 3633 Mini Circuit Tester
www.jbtoolsale...
Playlist
- (Chapter 1) Misfire ID, Compression Tests, Vacuum Leaks, Fuel Trim, Head Gasket, Restricted Exhaust, Low Power, DMM
• (Chapter 1) Misfire ID...
Related videos
- Fuse keeps blowing (how to locate a short to ground) - Mazda
• How to find a short to...
- Bad Alternator Diode causing transmission/speedometer problems
• Bad Alternator Diode c...
- How to test an alternator (Chrysler Dodge Jeep)
• How to test an alterna...
- Battery keeps going dead (what to test before replacing)
• Battery keeps going de...
- How to measure the current draw of your test light (Incandescent vs. LED)
• How to measure the cur...
For more information on this topic, I have written a “field manual” called Engine Performance Diagnostics which is available at www.scannerdanner.com as an eBook or paper book.
Want even more diagnostic training? Whether you are a DIY trying to fix your own car, someone looking to become an auto technician, or a current auto technician that wants to get more into diagnostics, subscribe to ScannerDanner Premium www.scannerdan... There is a 14 day free trial.
On ScannerDanner Premium I will bring you right into my classroom at Rosedale Technical College. You will find page for page lectures taken right from my book as well as exclusive classroom type case studies. What is so special about these classroom case studies? I pull live problem vehicles directly into my classroom and we troubleshoot them in real time, using and applying the theory and testing procedures we learn during the classroom lectures. There is no better on-line training of how to troubleshoot automotive electrical and electronics systems anywhere!
Disclaimer:
Due to factors beyond the control of ScannerDanner LLC, it cannot guarantee against unauthorized modifications of this information, or improper use of this information. ScannerDanner LLC assumes no liability for property damage or injury incurred as a result of any of the information contained in this video. ScannerDanner LLC recommends safe practices when working with power tools, automotive lifts, lifting tools, jack stands, electrical equipment, blunt instruments, chemicals, lubricants, or any other tools or equipment seen or implied in this video. Due to factors beyond the control of ScannerDanner LLC, no information contained in this video shall create any express or implied warranty or guarantee of any particular result. Any injury, damage or loss that may result from improper use of these tools, equipment, or the information contained in this video is the sole responsibility of the user and not ScannerDanner LLC.

[@GMAN420BC]

10 year old video but still relevant and still teaching DIYers such as myself. I sure appreciate you taking the time to post these vids throughout your career. You have helped more people than you know.

[@ScannerDanner]

Thanks so much man

[@keivanabdollahpour8737]

Well, for the ones saying why you didn't check the fuses first to find the problem, it's clear that you're not just fixing the car, you're teaching a field and are going down the list. That's what everyone needs to be shown for the sake of teaching. Appreciate all your knowledge being given for free in a professional manner.

[@ScannerDanner]

Thank you so much for seeing that about what we do. Really appreciate this comment.

[@CesarPerez-ck7ci]

I would never complain about your thorough tests Paul. I would much rather see a 2 hour video on a blown fuse than a 2 minute video on replacing a fuse.

[@ScannerDanner]

nice

[@notchback93]

Well said!

[@ironwill04]

Heck yeah! It has been my experience that it is rarely a blown fuse. It is always the real world issues.

[@tnamen1307]

@@ScannerDanner what is the charging output current from the alternator to the battery when engine is running?? Is it fixed at 1 amp or lower, or varies?? And, how does the alternator stops charging the battery when the battery is full?? Any sensors??

[@ScannerDanner]

@@tnamen1307 all done by a voltage regulator that is typically inside of the alternator

[@dmorley100]

WOW!!! I've been in this business 10 years now and I've never seen or heard of a alternator not charging due to a bulb circuit malfunction. Definitely gonna put that on my list of stuff to check from now on when I get an alternator not charging.

[@yougeo]

Thank you! This indicator lamp circuit test and its key triggering effect for the alternator to charge is SUCH A LIFESAVER to know for older Miatas! You are the ONLY mechanic to EVER suggest this!

[@ScannerDanner]

+yougeo thank you! just be sure it is an incandescent bulb in your test light and NOT an LED type.

[@theomnipresent1]

+ScannerDanner Why not use an led type? Does it have to do with resistance?

[@johnmckamy6398]

I know a lot but I'm like a lot of mechanics that never learned the specifics of electrical diagnoses and I find this to be the most in depth instructor . love the videos and thank you.

[@ScannerDanner]

Thank you!

[@scientist100]

Agreed, I know a lot of mechanics that are good at that, 'mechanical' things, they like to hear around the engine, touch tap but they will never go into troubleshooting mode. Visual inspection is great but one must know where to look and this is where the scanner comes into play. I have friends that ask me to scan their cars and find the problem with my expensive scanner and I just tell them that if it was that easy, then everyone would fix their cars (hence the parts changer was born, thanks to scanners).

[@mobilemechman]

Many thanks, Mr. Danner. Your videos have helped and continue to help me with my job more than you could know. I owe you the respect I have gained in my shop. Thank you!

[@tonyle7909]

I gotta admit Mr. Danner, you are a teacher for the present and future. I definitely honed my electrical off your videos and learning some different ideas you got going on. Speeds up my work big time at work! Cheers!

[@abcdefgh9138]

Great video as always! For me, the key point in this one was the customer saying the dash quit AND the car died. In addition to the great testing methods shown, I think this also shows how interviewing the customer is important. Keep these great videos coming!

[@cwj9202]

For educational purposes, it was excellent that you performed those checks before replacing the defective fuse. I would have added that the charge light circuit is grounded through the stator; thus, with key on, engine off, the light is on until the engine starts and the alternator begins charging, at which time the stator is creating voltage simultaneously removing the ground source for the charge light. Also, with KOEoff, the voltage reading on that circuit would be less due to the presence of the diode. Keep up the great work!

[@ScannerDanner]

+Chad Jessup thanks Chad!

[@spelunkerd]

That's a good link, to a great teaching site. I like the practice exams as a way to review topics.

[@tonymaciel1887]

hi Paul. Thank you for your video and your thoroughness. I'm one of those people that are learning a lot from you and your completeness on covering all the testing bases is truly appreciated. Thank you

[@ScannerDanner]

Thanks so much Tony! It is people like you that I have in mind when creating these videos.

[@ozzstars_cars]

I diagnosed a similiar problem with my '01 Subaru Outback, the #5 fuse under the hood would burn out sparatically. Alt. would stop charging, gauge cluster would die, engine would continue to run. I finally diagnosed the issue, there was a short in an aftermarket front turn signal connector. The loose brass contacts that power the bulb were touching together and popping the fuse. What a P I A! Problem solved with oem bulb connector installed. Great video once again, thanks Paul.

[@74bavaria2]

I really love watching your videos. Such a great explanation of how the alternator should work based on the wiring diagram. Every time I watch one of your videos, I always pick up something new, and able to use it on my own diagnostics. Thanks a lot.

[@YouTube.TOM.A]

Mr Danner. Every time you pull out a wiring diagram and trace the different components of the circuit you are performing a great tutorial . I share your enthusiasm for Mitchell diagrams and sometimes feel lost without it. Auto electric[s] used to be a separate discipline, but this is no longer the case.

[@colonialroofingofnorthcaro441]

Thank you for understanding that some of us do not know some of us are watching this and still letting you know what you're talking about in some things because they're used in automotive terms and we only know layman terms we would understand layman terms a lot easier than we do Automotive terms, but we're still willing to learn so that's the reason we take the time to specially come to this exceptional channel right here that really goes down the line and gives us a lot of information a lot of times it's it's overload information, but the point is we can continue to watch it over and over again until it all starts to make sense so thank you very very much for making these videos not just for those that know what they're doing but for some of us who know nothing about the electrics and cars and how they work and want to learn and that comes from a person who understand that and is really willing to make a channel how about the people who know but maybe they're missing some things but for those that know nothing and want to learn and keep growing in their knowledge to be able to understand how wiring and being able to check wiring in a car works so thank you once again

[@ScannerDanner]

wow what a compliment! way to go with your L1 bro. not an easy test to pass for a lot of people. thank you so much

[@dosequzla]

My hero, and I dont call anyone that easily. Im not done yet watching the entire video and I have 5 stars for you Paul, is it? My car is driving me crazy with a low voltage, no voltage and voltage drain even when the car is running. I've talked to so many 'subject matter experts' and they all give me the run around and dont even want to look at the car. I too had to get my alternator tested more than twice and even when checked ok I had them rebuild it from the inside out with new parts. I wasn't aware the alternator has to have solid ground connectivity through the casing to the chassis of the vehicle and although I've check there is at least some connectivity the fact that I painted the alternator bracket that holds it to the engine it may not be getting proper grounding. Also, my battery light is always on except today when i put a fully charged battery with at least 13.6v then the light went off but it came back up as my battery kept going down in voltage. I am almost sure now my issue is a wiring problem from the alternator and not the alternator itself. Thanks for not just stopping the video because you know what the problem is but explaining the situation to me a computer systems engineer makes a hell of a difference. My car is a rare SOB Dodge Stealth RT/Twin Turbo AWD, AWS, All Day Headache car but when it runs good it kicks but. Thanks for the information on this video. You've just got a new subscriber .

[@ScannerDanner]

Some hate my teaching style, but when you truly need to learn systems and operation and you're not just looking for a silver bullet, then you've found the right channel. Thanks so much!

[@mikehaynes52]

This is good training for junior high school learning. Guy is good beginner trainer.

[@Atacama777]

From now on you shall be known as the MASTER of the knowledge seekers.

[@ScannerDannerPremium]

lol thanks

[@nathanrhinehart597]

Definitely appreciate your knowledge and attention to detail. I had a automotive instructor in college that always told me (if you dont know how it works you can't fix it) you definetly bring that statement home with all your videos. Thank you for taking the time and effort to put out such detailed diag procedures.

[@elior77]

I took off the instrument cluster and then I noticed that I get no charge... I saw this vid and saved 200$ ! :) Thanks dude !

[@ScannerDanner]

+Elior Zeno sweet!

[@80ajflores]

You are soooo right about these situations with the car troubleshooting. I'm going through this exact same issue. Just trying to get my brain to retain your testing strategy. I wish I could take your classes. Very impressive work.

[@ScannerDanner]

Thank you! And you can online if you want! I have ALL of my classes recorded (over 540 videos now) www.scannerdanner.com/join-scannerdanner-premium.html Hope to see you there

[@ScannerDanner]

thank you! and I believe you are correct in that assumption about the resistor. that was my thought too! I have seen on other systems a blown bulb cause this so for others reading this don't always count on having a backup resistor like on this car

[@fredflintstone8048]

typically I check a fuse first, but it really doesn't matter which direction you come from, and it's always good to check the function of the alternator anyway, or at least know how to do it so this instruction is still very valuable. If the fuse is blown, then we know it blew for a reason, so yes, we don't send them away with the fuse replaced because it's going to blow again.

[@ScannerDanner]

Thanks Brian good to hear from you!

[@anotherhurayra2024]

I don't comment on youtube videos but my neighbour who swapped 3 alternators in my car yet he did not test the alternator correctly. I hope the bulb circuit is the issues in what is the cause for my cars issue. I like how thorough you were.. thanks.

[@ScannerDanner]

thanks for the link! this Toyota is a little different though. There is a 4th wire and this mazda only had three. I am sure it is similar though.

[@felplayvina]

Thank for the video Paul. This video is good lection why is important to use a diagram, many mechanic don't like to use it.

[@twiggy04072]

This video is one of the best I've come accross. Really good job. I noticed in the scematic that there is a resistor accross the charge indicator bulb, which I am assuming is there to keep the alternator working in case the bulb blows. This won't help with the blown fuse though.

[@ceedeegutierrez]

Level of detail is impressive Mr. Danner. Have you ever been accused of being a perfectionist like me?

[@RAFICKDAMISONMOYO]

I'm going to be not a part changer coz of you Paul, Thanks So Much

[@peterey2]

owe a huge THANK YOU, scannerdanner. had an accord in today that wasnt charging. check eng. light was on, customer said he tried a new alt-still didnt charge so he brought it in. i verified it wasnt charging, checked for + at the batt post and had power but i saw i didnt have power on the wire from the indicator light. found a blown fuse, replaced it-alt started charging. gotta diagram on that fuse-found it fed the heated o2, checked and found rubbed wire on the o2 from a misinstalled o2 sensor!

[@nestorfresno1]

good video like all the ones that you make...really good procedure to check the complete system key on and engine running always better to perform voltage drops... thanks paul..

[@DJChase007]

dude i have learn a lot from you. when i do alternator i use a test light to do most test its a quick easy way. use the test light to check the heavy gauge wire with the test light on ground we get we know that main alternator fuse is good. then you check smaller gauge wires. what i normally do is disconnect the connector in your case, you should find the test light for one of the wire when ignition at run. all alternator regulator the pin that goes to the warning send out negative as learn from you be component in this case the regulator. so with test on ground and touch the light if the gauge fuse is good the battery should come in the dash but you have to know your circuit

[@Element_lifestyle]

Scanner Danner: I tough that the white and black wire should have positive all the time while the car is running. Since the positive goes trough the light bulb. Unless its a a internal problem with the alternator, that is when the alternator give a ground to the light bulb and the light comes on.So i think seeing the 0.2 volts at the start on the diagnostic at the white and black wire, was an indication that we were missing the positive or having an alternator problem, but not saying the alternator is bad yet before applying a positive to the wire as you did.

[@tdracing13]

Awesome video Paul. As you said in your video you need to know how to properly test these vehicles instead of just checking fuses and shipping it. Thank you for taking the time to educate, I'm sure this eats up allot of your personal time.

[@SimplyDiagnostics]

You make a very good point re the “check the fuse” warriors. If all you ever shared was blown fuses none of us would learn from you Paul 👍

[@mckoylach1622]

Very elaborate procedures of charging systems test,great,thanks

[@rickchapman3707]

I am by no means as knowledgeable as Paul but i want to soak it up as much as possible. My old skool teachers told me if that light is not working at all on the dash find out why.

[@peterey2]

ya i couldnt believe the things i was checking that i remembered you doing in this video were so closely related to my 'real life' situation. the cat conv. that the problem o2 was in was welded in. when it was welded in, it was put at the wrong angle so the o2 wires were stretched bad to make connection to the connector on the car. the wire rubbed thru and actually grounded out on the o2 itself. gotta handshake from the boss for that diag, cant thank you enough!

[@humidbeing]

Fantastic video. Learned a lot! Never would have guessed bulb circuit.

[@dohc22h]

Thank you ScannerDanner... This piece of information is exactly what I needed to see right now. I had no idea.

[@stevewarren3051]

I learned something new today. Spend 17 minutes testing the alternator output before you spend 15 seconds to test a fuse. Thanks!

[@ScannerDanner]

Or spend 2 seconds and read the title and you'd see it says blown fuse in it. If that's all you were looking for, your in the wring channel.

[@christiantrezelle793]

thanks for this helpful video. I have been searching for a video that explains the importance of the battery light on the dashboard.

[@veejful]

Damn!!! )) I learn something new every time..I'm so high up on the ladder because of you P,thank you very much! GOD BLESS YOU!

[@londzale3163]

Tried All that fancy gadgets and tests just to find the fuse was blown. And then he tries to change the scenario like “but what if it wasn’t the fuse”. Know plenty of guys like these at the shop. This is a 5 minute job.

[@ScannerDanner]

You're right, I just like to hear myself talk.

[@Joeelectronicschematicsforauto]

I am so glad scanner that you finally came to the point of what I preach on my channel of automotive electronic schematics that people think one thing everything is the fuse problem and I preach that also if you think that you're never going to be an automotive technician you'll be a mechanic not everything is diffuse there are PCMs ECMs controlling the alternator outputs which people don't know too much about so glad you mentioned this point epic video

[@ScannerDanner]

good point, kinda went on a little rant there didn't I? just don't have patience for some of that but you are correct the majority of my audience, that comment was not meant for. and it is you guys that I truly value and I know you understand why I do things "the hard way" sometimes.

[@tectalabyss]

Hello Mr Danner. Your support is great on your website. Big thumbs up for his help. All my best. Bobby

[@ScannerDanner]

thanks Bobby!

[@peterreginella2906]

the guys asking why you didn't check the fuses first are prolly the same guys that would already have the alternator on order .... :) .... and if they're so wise why aren't they the ones making videos and helping other techs out on iatn such as yourself ...... and btw I have seen the bulb circuit cause the same problem on a lot of fords

[@ntorres586]

Very awesome video, I’ve learned so much from you Paul. Thank you for everything you do for us.

[@BrettyUK]

I got a truck to do once that wasn't charging someone had fitted an alternator. Batt light on dash. Not charging. After doin similar checks to you found an open circuit ign feed to alternator (that was a blown fuse). Had a dead short on that feed. Finally traced it to an electron headlight adjuster motor short circuit. Had me stumped for nearly a day.

[@bmw-e30]

Good explanatory video. The alternator recently failed in my BMW e30 but there was no charge warning light showing. The bulb is not blown. All ignition lights went off as normal when the car was started as if there was no problem but the battery wasn't being charged. Only indication was radio switching off and lights dimming. Something is obviously blown in the alternator which fools the warning light. The charge warning worked ok when I tried what turned out to be another dud alternator in the car. Anyway a new replacement alternator solved the problem.

[@camryle5590]

Great video Paul. I remember this issue in my Dad's Chevrolet malibu 1978 whenever the bulb was blown off the alternator didn't charge any more unless you activate the bypass circuit by snapping the throttle gently

[@khaniftikhar9225]

Very good demonstration

[@87Stang]

I love your vids I've learned so much from u especially when I get to use what I've learned from u out in the field n helps me find the problem fast n right the first time I tell every one about your vids your awesome keep it thanks

[@Joeelectronicschematicsforauto]

Exactly my point before I put in the fuse I measure from ground to see if I have a short I don't want to blow another fuse but you're doing a great job pool educating young guys I went to Lincoln tech in New Jersey and electronic school unless the only way to learn electronics properly and understanding computers or fuel ejection

[@marfmarfington]

Excellent explanation on everything you did!

[@gianfrancoa]

Thank you very much for the video, very educational. Ive done lots of electricañ works on cars and i wouldnt imagine that the bulb circuit would case the alternator not to charge. Great video!!!!

[@Freedomelectric]

I know this is a old video, but great video. Having exact same issue with my Toyota Highlander. I've gone to the auto parts store tobuy a battery then they said it was the alternator I will check these two out first.

[@jtcowhand]

Thanks Dan, I have learned a lot and now do my own work. 👍

[@ScannerDanner]

thanks man! what a great compliment

[@ScannerDanner]

Thank you Joel! God bless

[@ozzstars_cars]

So educational I had to watch this again......

[@sailorbob74133]

I'm one of those guys who didn't know it's that simple to check a fuse with a test light without pulling them.

[@traviswells1388]

I work as a supervisor for a large dealership, so I get to see a lot of new technicians and guys from trade and technical colleges come through the shop. I guarantee when they come to me about a electrical, or computer related problem my first question to them is --NOT-- did you check all the fuses first!!! My first question is for them to explain to me how the circuit is supposed to work, what checks they made and what the results were. Sorry if it sounds like I'm tooting my own horn or being a ass, but I feel that it's important the new guy and those that are wanting to build a career in the automotive or diesel related field understand that as a manager/supervisor if you don't understand electrical, not able to constantly learn, improve and progress your future is very dim, at least in the wages aspect of the job. As a result of this I thought it might be beneficial for the new tech to understand what it is like from the other side of the counter. Example: I gave a tech a job, customer complaint, " Blower motor doesn't work at times customer has replaced several fuses with no change, some times works and other times not." Happens every few days but more so when it's cold in the morning. Technician comes back 15 min later and reports with a smirk that was a easy fix what else do you have for me? What did you find I asked. "I couldn't find anything wrong so I installed a circuit breaker and parked the truck." Please don't be this guy!! If you want to impress your boss and learn something as well explain to him all the resources you used in making your diagnosis. Present the wiring diagram and the measurements you recorded during your investigation. Present any further questions you think would be appropriate to ask the customer that might be related to his issue. If you truly can't find anything wrong at least document were you would go from this point if the truck came back with the same complaint, based upon how the system works present other things that would be effected in the circuit(s), such as power is provide from the key switch to a 15 amp fuse that powers a relay, this relay in turn power fuse numbers xxxx of the fuse panel which provide power to the blower motor. If the customer has the problem again have him look and see if his horn doesn't work at the same time etcc...

[@ranstan4557]

you really something else

[@gabet3754]

I cant wait to see it. I had a similar problem with my 98 ford, it was a bad bulb.

[@jessesmith1181]

Paul absolutely perfect video and well thought out love the trouble shooting knowledge. Thank you very much

[@ScannerDanner]

thanks Mark!

[@juliomagdaleno7680]

scannerdanner your a beast. . .your a true master

[@ScannerDanner]

thank you rick

[@ScannerDanner]

Thank you!

[@windward2818]

It is interesting that the Alternator light dash circuit is needed for Alternator excitation (or perhaps voltage regulator enable), which I think is evident due to the resistor across the bulb, which provides a minimum feed resistance. I think the question to ask is why did the 15A Alternator / Dash fuse blow? For an intermittent fault, I would first suspect chaffing fuse output wire under the dash. Because to blow the fuse the short would have to be just after the fuse. To test for voltage drop on the Alternator main output B+ (heavy cable to the battery) you would really want to have "representative" levels of current (vehicle running current with loads on together with the battery charging current) output from the alternator, which depending on the vehicle, may actually terminate at a power distribution box and then go to the battery. If you monitor the Alternator current with a clamp meter and watch the voltage drop you could actually determine the overall resistance if you wanted to. One reason may be to see any difference in the circuit after you clean up any corrosion or dirty or damaged connections. I know I can look at these two channels with my Scopement, but I have not yet tried my PICO Scope. All that is really needed is the proper channel scaling (and isolated channels, unless a voltage differential probe is used) and a built in math function.

[@ScannerDanner]

In the description I have part 2 listed where we attack the cause of the blown fuse kzbin.info/www/bejne/fHychIeGaaxsY6s Thanks!

[@WizzRacing]

These types of alternators have been around for 50 years.. And the first thing we did at the Alternator shop was attach an exciter bulb to the alternator...As they require that bulb to excite the charging system...Then you find out why the fuse blew...

[@oscarrojas4281]

You are awesome teacher as you said it's not simple in the real life great lesson

[@ScannerDanner]

Glad you think so!

[@nigelclark7360]

Very good diagnoses

[@tpcoachfix]

Great job! Leave no stone unturned before coming to a conclusion and replacing parts unnecessarily. The bulb circuit "excites" the alternator, without it, it won't charge.

[@marioalanis1855]

I learned something new today thanks

[@mckoylach1622]

Great video,very elaborate procedures of how to diagnose step by step tests,thank you,Paul. Anyways,without a wiring diagram,how do you know which wire to test because there three wires on that connector,to the alternator ? Is there a color code that indicates which wire does what function? If you don’t mind explain,thank you

[@MarioDallaRiva]

Hey, hey, Paul. Awesome oldie but goodie! ?: That bulb circuit diagram is showing a diode I believe (WHT/BLK) and a resistor in parallel with the bulb. Can you please confirm I'm interpreting that correctly? I love the way you always follow through with additional voltage readings as you did throughout this video! I helps to solidify what's being learned from your case study. I tried looking for comments below asking about the diode but I didn't see any in the ones I went through... Thanks!! Hope you and the family are all doing well. Ciao!

[@ScannerDanner]

Time frame please. Thank you!

[@MarioDallaRiva]

@@ScannerDanner Hi Paul. 1:02 the wiring diagram of the instrument cluster bulb wiring shows a diode symbol between the bulb and external connector WHT/BLK. Also, a resistor in parallel with the bulb. Is that in case the bulb filament is severed? Thanks again!

[@ScannerDanner]

Nice! What are the chances of that.

[@jimbuford4147]

I see a couple of guys explained what makes the inst light go out when it cranks but it went over my head. Can you help me on this point. As usual a great video. I always learn so much from yours and to me the longer they are the better. Thanks.

[@ScannerDannerPremium]

+Jim Buford thanks Jim. Hard to do here but in short what makes the light go out is when there is equal potential on both sides of the bulb. 12v from ignition switch and ground through alt. When it's not producing voltage. Once alt begins to spin it puts voltage on that circuit that was a ground. Light goes out. Remember if a bulb has 12 and 12 there is no flow

[@Autokey_Security_Services]

Should have showed the power distribution diagram and focused on why the fuse blew.. Fuse blew for a reason it will just blow again. There could be a corroded wire opposite of the meter fuse that intermittently grounds to chassis when car is being operated.. Either way great video!!

[@ScannerDanner]

I have that in another video Fuse keeps blowing (how to locate a short to ground) - Mazda kzbin.info/www/bejne/fHychIeGaaxsY6s Thanks!

[@josenildosilva1064]

hi i would like to tell you thank you so much for your videos, i had learned a lot. i do not have enough word to say thanks, you are the best. Moura

[@1mw4tch1ng]

If you are a mechanic and charge by the hour then proceed with all these steps of testing voltage drops etc. If you charge by just fixing the issue then just check the fuse since no cluster lights, etc, and fix the issue instantly.

[@OP-ik7qb]

Paul thank you so much for this one. GOD bless you

[@prmayner]

I think they call that an exciter wire. I remember my first with this. I put a gm alternator on a F100 cause they were so easy to rebuild and i had to run that wire with an inline bulb to get the alternator to start charging. Damn that seems like a million years ago, wait maybe it was. ha ha Good Job Danner.

[@rickbauza]

paul you have to learn how to crawl and walk before running.what am saying is learn schematic for the specific system. now if you know what and how system works youl know how to fix ir.great video my friend sorry about those lacking knowdledge in the automotive industry.thank you have showing us more knowdledge than wahat we already know.i have 30 years under my belt with a master status and L1 cert whish wasnt easy to pass.in this great industry you never stop learning.thank you greatly rick.

[@amirkhanozniev1]

i have 2 questions: 1) why does alternator need feed from mainrelais or why would alternator feed mainrelay? does it not get its D+ from cluster? 2) When u use testlamp and the alternator starts werking why does it stop charging when u takes testlamp away, is this circuit not needed ONLY for startup? Thanks!

[@plowe6751]

I once saw a 2000 Mitsubishi Eclipse get 3 replacement alternators installed for this exact same issue. Blown fuse for the dummy light.

[@ronaldravenscroft3431]

It gives you a little more knowledge of how alternators works and how to repair them. Don’t always take the easy way . We all can learn something from this experience. Ron

[@ShiversRSS]

Never knew that was possible. Thanks. Love your videos.

[@gvvq-pi5ml]

Hi Paul and others, the warning light terminal on the alternator provides an earth for the warning light, earth goes through the brushes, rotor and regulator to ground, light comes on, when running 14 volts shoots up from that terminal, from the rectifier, to warning light, so you get 14 volts each side of bulb, so it goes out.. i had one guy years ago that fitted a new battery, alternator and starter, and the battery still went flat, i said does the warning light work, he said its not on, i said but does it work at all, he didnt know, anyway i put a bulb in it and cured the probem...expensive for him just for a bulb...Fred in Uk.

[@frankrojo1741]

Hey there I know that damn good video I don't care what the haters say your students i lucky to have a damn good instructor like you

[@ScannerDannerPremium]

Thanks Frank!

[@sivucit]

hi paul, I happend to watch a video about that Alternator especially on internals of electrical cirucit. The charging light gives power to the regulator, this regulator have a built in pulse width modulator which will pulse the field coil(on and off) the field coil, during high speed pulse is less and vice versa, once the car started, operating generator causes the charging light to go off by disabling the ground to that light. continued...

[@gvvq-pi5ml]

You can get those test lights off ebay now for about £2.50, that's about $5 i bought 2 of them....yes inside the alternator the bulb circuit usually goes through the rotor, then through the regulator to ground, so when you turn the ignition on the light comes on, then when it starts there are 3 field diodes connected to the terminal inside so you get battery voltage on the bulb wire when engine starts, so you end up with 12 volts each side of the bulb...you can just earth the bulb terminal out to see the if the light comes on that's a good test on the light and wiring.....from Fred in England.

[@chuckodonnell1894]

Thanks for all your help !!!! you ROCK!!!!!!

[@ScannerDanner]

thanks tom

[@javiertorres9209]

thank you for your video. thanks for this video i can fix my cousin's truck today is 00 ford ranger 2.5... thank you very much