Generator - How to Bench Test it While in your Car (Newest Version)

Battery charging issue seems to be a common problem with our vintage British cars. Here the Moss Motors Tech specialist walk you through checking your generator to see if it is functioning properly. Does the problem lie in the generator, wiring or voltage regulator. This video will help you eliminate one of the culprits. See our How to Test your Voltage Regulator to get the rest of the story.

[@TheRadioStu]

A candidate for one of the best DIY videos I've ever seen. Clear, articulate and a great delivery. My Nuffield diesel tractor is charging again. Thanks!

[@F.Krueger-cs4vk]

👍🏻👌🏻

[@wiggymccrackin8240]

that was probably the best explained video I've ever seen. you really covered everything.

[@F.Krueger-cs4vk]

👌🏻👍🏻

[@kenmayfield3739]

It would be really useful TO ACTUALLY BE SHOWN THE TERMINALS !!!!!!

[@speedfinder1]

I'm in my fifties and have been working on my own classic cars since I was ten years old. I wish someone had taken the trouble to explain to me how simple this stuff is, all those years ago. I've spent a lifetime not working on charging systems because "Those who knew" were happy to make money from me! NOT ANYMORE!

[@alexanderleed1]

You re probably the best teacher I have ever listened to. Straight, clear and concise. Thank you!

[@Robelixxx84]

I like your smooth & calm voice while explaining. Could listen to you all day, great explanations, great stuff. PLEASE keep on doing, greetings from Austria :)

[@riv1950]

This was what we needed, thank you very much.The best explanation I have seen on DC generators.

[@clifftonicstudios7469]

Best teacher ever amazing explanation great video on white helps to see immediately subbed.

[@integrityautocarehomeofthe145]

AWESOME! I specialize in electrical and we have a 1962 Cadillac Eldorado with a GEN light on, and I'm ready to do some testing now! Thanks again for the GREAT video! DRTCD over and out...

[@user-tn1hk6zm2freedom]

I have one that motors great when I put 12 volts to the armature slows down quick when power is switched to the field coils but will not charge. New bushes cleaned the armature new voltage regulator. Makes .10 of a volt. I have done all the tests and seems fine. I am puzzled.

[@ianrobinson9565]

A good video for the amateur. However people get into trouble when they don't know and they don't understand whether their generator has an internally earthed field or an externally earthed field. Never polarise your generator from the regulator box. Remove both the wires from the generator and polarise the fields at the generator. You will need to know whether the generator has an internally or an externally earthed field. If you try to polarise the field at the regulator box and it is externally earthed field, then you are shorting battery to earth if you tap the field terminal instead of the dynamo terminal.

[@JAC-bn9ts]

At 2:40, you give the instruction to take the one end of the test lead to "the brown wire that feeds your voltage regulator". After almost 70 years of dirt and grime, all my wires are "brown wires". Can you please specify which wire from the regulator you're referring to? I'm guessing A (off the 5 point regulator). Can you confirm (or correct) this? Thank you. Alternatively, can you attach the test lead to the positive battery terminal? Should the car be on or off during this test?

[@trevorseals6588]

I don’t see why you hook the field winding ti the battery along with the output wire for the motoring test. My service manual tells me to ground the field post. Could it just be how my generator is wired internally?

[@LubaLuba1]

I am a little confuse because you connected a negative wire to D and field wire connection should this be positive side of battery and you got ground to positive hmmm ??

[@rdmanone]

Good video

[@skipast75]

Thank you for this! Got my 64 Corvair back in the road in no time.... All I had to do is clean the grooves on the armature

[@drew20121]

I'm trying to troubleshoot my 1964 corvair too!

[@bambiajkorakim9416]

well done, like this video.

Going the way of the dodo... Nice I learn an new idiom.

[@JamesBrown-126]

How do I polarize my generator ?

[@anthonykeri9343]

Great video! 1969 MG Midget: I first tested the generator using the University Motors method of disconnecting the battery with the motor running at 1500rpm and the headlights on. Motor continued running no problem and headlights didn't even dim. But with your bench-test-in-car method, I was only getting 10.5-11 volts from the generator at 900rpm. Does it need to be replaced/refurbished? I am having increasingly frequent dead battery incidents (battery is 2 years old and Pep Boys says it tested fine). Thanks!

[@bluesman914]

Fantastic, Thank you for sharing this. Really appreciate good info like this.........MM

[@garybeck-t3v]

This dude has the creepiest voice I've ever heard.

[@oriocoookie]

how can one tell which is teh D and which the F terminals?

[@PirahnaStudios]

Great explanation. What if my generator spins, but voltage is between 0,08-0,13 V? What should I check next?

[@mbmpablo3631]

I have the same problem did you find a solution?

[@PirahnaStudios]

@@mbmpablo3631 Unfortunately no. I gave it to specialists and they only told me, generator need to be regenerated.

[@duane3719]

Simply amazing. So well explained and so clear. Thank you

[@westonlee9982]

good info thanks

[@Antonnick]

Makes it all very understandable. I would say however, and others have confirmed this, that the voltage reading when shorting the F and D with the engine idling does not go above 6V. Only when revving the engine up will it increase to the 18V or more. Perhaps this is because my own Dynamo is quite old and in need of refurbishment but I surmise, that is the case for most people these days.

[@shadetreeautomotiveenthusi1284]

Great explanation, great video, and no offense, but you sound like George Carlin on Thomas the Train with a splash of Bob Ross. Did you smoke before you made this or pop some Valium? Anyway, still, great video. Tap, tap, taparoo.

[@robertruggles5584]

I wonder if you have answers to my questions. I have an 8n Ford tractor, 6v positive ground. I believe the generator is 8N10000c. It's 2 brush and externally grounded. Has ground, field and armature terminals. Regulator has batt, arm and field terminals. Engine stops when battery cable is unhooked. I can run it as a motor. But with engine running I'm only getting like 6.27v. I'm unable to check voltage with a meter as you did by jumpering the terminals on the generator. Is there another way to check the output of the generator? I can hook up meter leads to arm and ground posts on generator. At about 800 rpm I get about .7 volts. If I raise the rpm to 2200 I'm getting about 1.3 volts.

[@dwest4297]

Thank you so much for making this video. It was one of the best DIY videos I've seen and help me figure out that my generator was working (yeah).

[@F.Krueger-cs4vk]

👍🏻👏🏻

[@bobvansand6346]

Thx, interesting lesson! Bob the belgian😬

[@austinwagoncompany]

Good video, the rebuilders in my area didn't want to share info like this and I suppose they're afraid of the possibility of getting competition so it's understandable.

[@deanludwig1525]

Great video but note output test this way only works for internally earthed fields. If your regulator grounds the field then you need to put the field terminal to ground to get full output.

[@robertruggles5584]

I wonder if you have answers to my questions. I have an 8n Ford tractor, 6v positive ground. I believe the generator is 8N10000c. It's 2 brush and externally grounded. Has ground, field and armature terminals. Regulator has batt, arm and field terminals. Engine stops when battery cable is unhooked. I can run it as a motor. But with engine running I'm only getting like 6.27v. I'm unable to check voltage with a meter as you did by jumpering the terminals on the generator. Is there another way to check the output of the generator? I can hook up meter leads to arm and ground posts on generator. At about 800 rpm I get about .7 volts. If I raise the rpm to 2200 I'm getting about 1.3 volts.

[@chrisniederkrom2490]

Found this out the hard way! Took my generator to the rebuilder and he said it was fine. Glad he’s an honest guy!

[@clarkede]

Great descriptive video!!!! I have a 1948 Plymouth with a 6 volt positive ground generator that looks the same as the one in this video... HOWEVER, I just took it apart and cleaned it all up and then tried to test it as a motor as described in this video. It did NOT work. I was concerned that the generator was bad, so I called a local repair shop (that specializes in starters, alternators, etc.). They told me to bring the generator over and they would test it quickly for free. I hopped in the car and took it right over to them. They tested my generator for free and said it works great. Whew... I was relieved. I mentioned this video to the technician and asked if I should be able to put a jumper between the A and F leads and then properly connect the battery (+ and -) and it should run as a motor. The technician said that was wrong for my generator. Instead, he said that I would need to jumper the Field (F) terminal to the ground (in my case Positive, since my car is positive ground), and then connect the battery (in my case the negative terminal) to the A terminal - and then it would run as a motor. I just wanted to mention this to future readers in case their generator is wired slightly different. I hope this helps someone.

[@Chiaroscuro1991]

Thank you so much. I must fried the “cutout” (used before voltage regulators) on the generator on my 1923 model T Ford. I made the mistake of continuing to drive the car and killed the armature as a result. Got a donor armature and replaced the dead one and wanted to see it it worked. Hooking it up to a DC power source made it run, so one test done.

[@marvinzelikovic4493]

1-how do you know your car is negative or positive ground 2- how do you lower your RPM

[@flyingdutchman44]

follow the battery terminal that connects to the body/chassis.If it's the positive on the battery it's positive ground and vice versa.

[@austinwagoncompany]

Idle screw on your carb or take the vacuum hose off of your vacuum advance (and plug it) or if you have an older fuel injected car you can jump two pins in the ecm connector under your steering column, you'll have to figure which one's on your own, I did it on my '88 s10 to set the timing but don't remember which one's they were and I'm sure other cars are different anyway.

[@ichhasseamerika]

Anyway, if u get the +/- ground wrong, the voltmeter will just show negative number instead of postive, right? (point being that its the number thats important) Is my logic sound there?

[@philliphall5198]

Follow the battery ground wire

[@flyingdutchman44]

great video ,simple, clear and concise

[@laurentiuprisacariu9905]

wow instant subscribe

[@johnobiro5202]

Brilliant, very well explained.

[@philliphall5198]

This really makes me feel old because I’ve rebuilt a lot of them back in the 60 in shops and turning them down

[@FarmDad]

Top notch video. You are a natural teacher.

[@pnorfy61]

Excellent help - thanks

[@zensurfer55]

Fred Flinston's neighbor and the Wright Brothers; great analogies! And, I guess if that will work on classic British cars it should work on my classic German vw bug! Thanks

[@dfishpool7052]

Excellent presentation - many thanks.

[@cliveblunden5613]

Really great video, well explained, my project, a 1936 Vauxhall/Bedford ute is now charging for the first time, can't thank you enough.

[@jedtayloruk]

A perfect presentation. Very clear and the hand gesticulation really helps to emphasise what you are saying. Bravo.

[@Bikeaddict4235]

Excellent

[@carlolisadangelo2854]

outstanding !

[@jefftaylor728]

Very well explained. And this guy needs to be hired to read books on tape of some sort of voice work. amazingly calming voice. A doctor with this voice could tell you that you only have 6 months to live, and you'd be ok with it!

[@BrownianMotionPicture]

Great explanation.

[@hueyhoolihan582]

these videos are "...gold!, Jerry, GOLD!". :)

[@cobbadog]

thank you for a very good video and description on testing the generator

[@333Roulette]

This is the best video I have found on this topic. I have a 58 Chevrolet Corvette that has stopped charging. This video has given me a clear instructions to narrow down my search as to what component may be not working. Thank you for taking the time to make the video!!!

[@imrehegedus3804]

Awesome video! Great explanation. Cheers from Japan

[@paulsteele5472]

This is really well explained and I’m off to test the dynamo in my Land Rover confident in being able to see if it works properly. Thank you

[@rafaelprdm4]

testing a 1960 Eldorado Biarritz. I did the test and it failed. to witch terminal do i connect a condenser. i found it close to the battery terminal.

[@enriquearroyo3408]

My generator only produces 2v.

[@AristocraftBoats]

Great video!! Just learned a lot. Thanks

[@robdoe2420]

X2 on all the positive comments.

[@gregb91401]

Genius - thank you for making this video.

[@ivanpanayotov1702]

i did the first test. the generator rotated. when i did the second it didn't generated any voltage. any ideas?

[@grahams_number]

Brilliant video, Thank you

[@annepoynter6600]

What a fantastic channel ,thank you.

[@taijlallbrij5764]

i need to know if this type of generator can make a wind turbine

[@woodpig41]

you sound like neil degrasse tyson

[@buddyletendre]

Thank you for the video, by far the easiest to understand and most in depth out there. If my generator fails the motoring test does that mean it’s no more than junk to be swapped as a core? Or is it something I can rebuild myself?

[@earlrose2084]

Mostly they were just brushes going bad,did a bunch of them

[@christinemazurek7925]

why did my wire spark when i touched the jumper

[@christinemazurek7925]

my generator has an A terminal for Armature & an F terminal for field what terminals do you have in your video testing ?

[@garygilmore4670]

Do you know Bill Walton?

[@836dmar]

Excellent presentation

[@sampsonrover]

The bob Ross of dynamos.

[@dalegribble60]

well done! But will this work with a MALE generator?

[@zesty2023]

thats a sexy little generator isn't she? : P

[@chevyengine307]

Still confused

[@paulaustin7352]

great video

[@flipper184]

Thanks.

[@edwinkinney1936]

Yes, that was an excellent DIY explanation for testing a 6 V generator !

[@F.Krueger-cs4vk]

27 thumbs down, pay a tech.

[@sarahcalder513]

This video is some what helpful although, testing my generator in my car is not working, I can get it to spin like you do in the video, but when its on the car, it doesn't give any voltage.

[@robertruggles5584]

Same here.

[@laredokarl]

Saner here, too

[@1964JEDAGI]

Put a dot on the pulley. I didn't see it do anything.