The EASIEST way to test parasitic draw

In this video, we’ll show you the best and easiest way to test for parasitic draw in your car. We’ll take you through all the steps needed and show you how to quickly find the cause.
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How to Test a Car Battery With a Multimeter:
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Reasons Your Car Battery Keeps Dying:
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Chapters in this video:
0:00 Intro
0:13 What is parasitic drain?
0:36 What you need
0:46 Turn off electronics
1:13 How to measure
2:26 Finding the cause
4:03 Fixing it
4:19 Outro
Disclaimer:
Due to factors beyond the control of Classic Car Maintenance, we cannot guarantee against improper use or unauthorized modifications of this information. Classic Car Maintenance assumes no liability for property damage or injury incurred as a result of any of the information contained in this video. Use this information at your own risk. Classic Car Maintenance recommends safe practices when working on vehicles and or with tools seen or implied in this video. Due to factors beyond the control of Classic Car Maintenance, no information contained in this video shall create any expressed 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 from the information contained in this video is the sole responsibility of the user and not Classic Car Maintenance.
#parasiticdraw #howto #ccm #multimeter #carcleaning #cardetailing #autodetailing #detailing #carcleaning #detailingchannel #detailingtips #detailingtutorials #classiccarmaintenance

[@classiccarmaintenance]

NOTE: If you have a modern car with electronics or accessories that need continuous power supply to not lose data and settings, you need to hook up these electronics and/or accessories to an external power source to power them before disconnecting the battery. Always first check your car's owners manual and your car accessories' owners manuals for instructions. However, it’s important to know that if you use an external power source, you won’t be able to tell if the parasitic draw comes from any of these hooked up accessories or electronics.

[@stevet603]

I disconnected the positive from the battery terminal to the fusebox at the battery terminal. I thought the problem might of been where the cable joins under the fusebox, but couldn't figure out how to remove the box to inspect the underneath. I think I have an alternator issue, because as soon as I squirted some (lots) of WD into it the multimeter started reading milliamps instead of amps. A couple of days left overnight the battery showed as 12.68V so thought I had tracked it down, but today it was down to 12.35V (after locking up and leaving for an hour).

[@classiccarmaintenance]

@@stevet603 WD40 is an insulator fluid, meaning that it can temporarily solve an issue with an internal short somewhere in your alternator. If the WD40 fluid gets in between two rubbing wires or a damaged wire and a metal surface which cause the short/parasitic draw, it can temporarily solve/mask that issue. The first and easiest thing you can do to see if you have an alternator issue, is to disconnect your alternator right after having measured your car battery voltage. Then leave your car locked overnight with all electronics turned off, and measure the battery voltage again in the morning. If your battery voltage is much lower than the previous day, your alternator probably isn’t the (main) cause. If your car battery reads about the same voltage, it’s highly likely your alternator is faulty and needs to be replaced. In case this test indicates that your alternator isn’t the (main) issue, the next thing on your checklist, based on your findings, should probably be to find a way to disconnect and test the cable between the battery terminal and the fusebox. IMPORTANT: Do not attempt to start or drive your vehicle while your alternator is disconnected, as this could damage your alternator!

[@stevet603]

@@classiccarmaintenance Thanks for that. some days, it holds 12.6V, other day down to 8V overnight. where do I disconnect the alernator please?

[@classiccarmaintenance]

​@@stevet603 Disconnect all electrical wires that connect to the alternator, but make sure to first take pictures so you can reconnect them exactly as they were afterwards. Careful: do not start the engine or drive your car with the alternator wires disconnected to prevent damaging your alternator.

[@KC9IUX17]

No change up, no curveball, nothing but FUCKIN GAS GOAT

[@mark-1rc502]

Thank you for the most easiest non tech nerd way of explaining how to do it . 🙏

[@classiccarmaintenance]

Thrilled to hear you found it easy to follow! Thanks for the support and happy motoring!

[@tonymaxwell9460]

Hell yea!! Finally, a video I can understand. Thank you!

[@classiccarmaintenance]

You're welcome! Glad you liked it!

[@jerrydavis6995]

​@@classiccarmaintenance@classiccarmaintenance I

[@HughDuncan-od8sq]

Beautifully done, thank you, now consider myself an expert in parasitic draw...

[@classiccarmaintenance]

Thanks! Glad you liked it!

[@ThadeousMonkey]

Thank you!!! I watched several videos for this and you best described what to do and what to look for.

[@classiccarmaintenance]

Glad you liked it!

[@razvanandreiparamon7762]

Thanks man, really helpful and straightforward

[@classiccarmaintenance]

You're welcome! Glad you liked it!

[@bobkernahan6340]

great video and to the point thank you

[@classiccarmaintenance]

Thanks, appreciate it!

[@CalebHigginbotham]

very informative and condensed video. thanks!

[@classiccarmaintenance]

Thanks! Glad you liked it!

[@foggymtnbreakdown]

Your meter may confuse some viewers who have a different meter. On your meter, the switch is turned to the symbol for AC amps, which has the sine wave line under the solid line, but the digital display shows DC amps, which has the symbol with the dashed straight line under the solid line. I have 3 multimeters where the rotary switch can be set to DC amps or AC amps. If I did it like you did it on the video, I would be trying to measure AC amps instead of DC amps. I am assuming that the "func" button on your meter selects between AC amps and DC amps. Your video helped me a lot. Thanks for taking the time to post it!

[@classiccarmaintenance]

You are correct! Our multimeter has a single symbol for both AC and DC amps, which we can switch between by pressing the FUNC button. If you have a multimeter with seperate symbols on the rotary switch, you have to turn it to the DC symbol with the dashed straight line under the solid straight line. Thanks for the feedback!

[@alext8828]

Excellent video. Very clearly explained.

[@classiccarmaintenance]

Glad you liked it!

[@ronaldochambers1107]

An excellent video, brief but detailed. I understand with modern cars with their numerous computers it's even better to check for any voltage drop across a fuse using a second multimeter across the small terminals on each fuse. Thus the fuses are not removed which could "wake up" any computers which take a while to "go to sleep" when the fuse is replaced.

[@classiccarmaintenance]

Hi, Thanks for your reply, appreciate it! You’re absolutely right that there are other ways to test for parasitic draw, like measuring and investigating the relation between voltage drop and current draw by testing over the fuses while in situ. However, this involves testing and calibrating your test equipment before you start, researching “normal” power consumption of each circuit on your specific vehicle (taking into account aftermarket equipment), closing or latching all door locks and avoiding anything that might trigger a sensor that could “wake up” the car’s computer(s). To be absolutely sure that the computer(s) are “asleep”, with the latest cars you might have to wait up to 2 hours. To interpret the readings you get over the fuses, you would have to use a comparison chart, specific to the type of OEM fuses that are used in your vehicle. Aftermarket (replacement) fuses that often look exactly like the OEM ones might give different values and will be hard to guesstimate. That being said, these tests are very specific to the brand and model of your vehicle and to do it right, you need access to the correct information and experience with this exact type or family of vehicles. Our aim is to empower people on how to do a basic DIY test for parasitic draw that anyone can do, with a small budget using a simple cheap multimeter, without needing expensive equipment. Although it’s a basic test, and it may not be perfect, it gets the job done and it will eliminate all major parasitic draws in minutes.

[@kennydiel4797]

Great video, simple to the point. Easy to understand. Finally not all the hoo-ha bla bla bla stuff.

[@classiccarmaintenance]

Thanks a lot! Glad you enjoyed the straightforward approach. Appreciate your support!

[@oncallguy]

thank you

[@classiccarmaintenance]

Glad you liked it!

[@jameswalley7234]

I had to open my door to get to the fuses, which jumps the lights and then waited for them to stop to get an accurate reading. I pulled a fuse for my seat and saw a change but after putting the fuse back the reading was normal.

[@marifkhan2003]

How we can bring hybrid car in accessories mode without connecting negative battery cable? Or is there a different method to test amps drop in hybrid cars?

[@classiccarmaintenance]

Thank you for your question! For hybrid cars, due to the complexity of their electrical systems, it's best to consult a professional licensed mechanic who is trained on your specific brand and model. They have the specialized knowledge and tools to safely and accurately diagnose and address any issues, without causing damage.

[@kr2731]

What if you need a certian accessory to be on all the time? Like a third party car alarm, gps tracker and dashcam running the continous draw from the battery?

[@classiccarmaintenance]

In that case you need to hook up these accessories to an external power source to power them before disconnecting the battery. We like to use a car battery charger that has a supply mode like this one amzn.to/3wxSJRg. Always first check your car accessories’ owners manual for instructions. However, it’s important to know that if you use an external power source, you won’t be able to tell if the parasitic draw comes from any of these hooked up accessories.

[@bivideo7]

Read mV drop across fuses...

[@DetailDuck]

If I hook my multimeter up like you did, should I still be getting power to the car?

[@classiccarmaintenance]

Yes, the power will run through the multimeter but will be limited by the fuses inside your specific multimeter. If the power demand surpasses the capacity of the fuse(s) in your multimeter, the fuse(s) will blow. For example, this can happen if you try to start your car.

[@stevet603]

I have a reading 0f 4.8mA (no matter what the setting on the multimeter the decimal point doesn't move?doing this) .I can't turn the ignition to accessory position to test the a draw increase as not even the dash or interior lights come on with the battery cable off, let alone the radio?

[@classiccarmaintenance]

There is no need to turn your key to the accessory position to test for parasitic draw. You should test this with all electronic components and accessories turned off and wait until the computer goes into sleep mode if you have a modern car. In our video we turned the key to accessory mode with the radio on to simulate a parasitic draw for demonstrational purposes, as our car did not have electric issues.

[@stevet603]

@@classiccarmaintenance Hi, new starter motor fitted. Today I tried removing all fuses one at a time with the multimeter in series on the neg cable. With car shut and locked, (apart from bonnet). After a while I got a 0.35A to 0.15A draw. Removing fuses one at a time (from all 3 fuse boxes), didn't do anything. Removing the positive feed to the alternator (from the battery terminal) didn't do anything, (did this checking for a shorted Diode causing drawback). The only way it totally disappeared was by removing the Positive connection to the engine bay fuse box; But that just made it read as zero. I don't know what else I can check now?

[@classiccarmaintenance]

Hi, could you specify if you disconnected the positive cable to the fuse box at the battery terminal or at the fuse box?

[@Artur-Itas]

INTERESTING SOMETHING HAS BEEN SEVERLY DRAINING THE POWER FROM MY CAR BATTERY LIKE A VAMPIRE IN THE DESERT. THE BATTERY CAN'T HOLD A CHARGE TO SAVE IT'S LIFE. HOPEFULLY THE MECHANIC CAN FIX IT, CAN'T WAIT TO FIND OUT THE CAUSE. IT IS SO ANNOYING.

[@tiffanyv4205]

Did you ever find out??

[@user-tg3bn1qh5t]

Hello I'm trying to setup my multimeter to the correct setting.on my multi meter mine doesn't have the A-~ but it has the 10A-~will that still work ?

[@classiccarmaintenance]

Hi! Yes this should work just fine if your multimeter can measure milliamps in that setting. Put it on 10 amps if this is your multimeters' highest setting and see what it reads. To get a more accurate reading, if your multimeter has multiple amps settings, then select the amps setting just above the parasitic draw your multimeter is reading.

[@user-tg3bn1qh5t]

Thank you also when I plug the red leed into the 10A hole it doesnt get any readings. The voltage frequency hole(max 300v) gets readings with the red lead will that still work the same ?

[@classiccarmaintenance]

No, you need to measure amps, not voltage. Sounds like your multimeter isn't sensitive enough to measure the parasitic draw or is malfunctioning. Even if your car doesn't have a parasitic draw, your multimeter should measure some milliamps, never a zero value.

[@user-tg3bn1qh5t]

Hello I bought a new multimeter with the correct settings . It.shows a 1.39 draw on the multimeter and right away the horn started going off . Am I doing something wrong ?

[@classiccarmaintenance]

It's impossible to tell what's exactly going on not knowing the setup of your specific car, but chances are you set off your car alarm by disconnecting your car battery. This could in turn activate your car horn. This would also explain the 1.39 (amps?) draw your multimeter is reading.

[@zeeshawnali4078]

In one shot you have the negative lead from the multimeter on the battery terminal and another you have the positive, does it matter which way you do it?

[@classiccarmaintenance]

No this does not make a difference. It will only change the "direction" electricity flows through the multimeter, displaying the parasitic draw as a positive or negative number. It does not change the measured value itself. If you connect the multimeter between the negative battery terminal and the battery cable with the black test lead on the battery terminal, it will display the parasitic draw as a positive number. Put the red test lead on the negative battery terminal and the black test lead on the battery cable and it will show the exact same parasitic draw, but as a negative number with a "-" sign in front of it.

[@zeeshawnali4078]

@@classiccarmaintenance thanks!

[@citymarine7256]

How does the radio turn on when the battery is disconnected?

[@classiccarmaintenance]

With the multimeter forming a bridge between the negative battery terminal and the negative battery lead, there is enough current passing through the multimeters' test leads to power the radio and other small accessories. However, the amperage is limited by the capacity of the multimeter itself and its internal fuse(s).

[@gegervary]

How does the radio in the car turns on if the negative lead is off? 🤔

[@classiccarmaintenance]

With the multimeter forming a bridge between the negative battery terminal and the negative battery lead, there is enough current passing through the multimeters' test leads to power the radio and other small accessories. However, the amperage is limited by the capacity of the multimeter itself and its internal fuse(s).

[@shimanoo11]

Do you need to lock the car first?

[@classiccarmaintenance]

You don't need to lock the door. Just closing the door is fine, unless the parasitic draw is in the locking system, but that's highly unlikely.

[@shimanoo11]

@@classiccarmaintenance Thank you so much!

[@XpertHeadyVids]

You said to keep doors locked all time. But you opened the door to get in to the fuse box, wouldn’t that mess up the test?

[@classiccarmaintenance]

That’s a valid question, you have a good eye! If you have to keep your door open to film the testing process like we did, or because the fuse box can only be reached with the door open, you want to manually lock the door locking mechanism or tape off the door jamb light switch to prevent keeping the computer(s) awake and to shut off the interior light(s). If you manually lock the door locking mechanism with the door open, do not forget to unlock the locking mechanism before slamming the door shut though! It’s a good idea to put some tape on the door or on the door handle as a reminder. Because our ‘98 Wrangler only has a very basic ECU, it does not “lie awake” (pun intended) over an open passenger door. We just removed the only interior light bulb to prevent it drawing current.

[@XpertHeadyVids]

@@classiccarmaintenanceokay got it thank you! Great video btw!

[@donmiller61]

I guess with classic cars you don't worry about wiping out the car's computer memory (for whatever it saves) by pulling off the ground cable.

[@classiccarmaintenance]

You’re absolutely right, disconnecting the car battery is not an issue with old school cars that don’t have advanced electronics or accessories. However, If you have a modern car with electronics and/or accessories that need continuous power supply to not lose data and settings, you need to hook them up to an external power source to power them before disconnecting the battery. Always first check your car's owners manual and your car accessories' owners manuals for instructions. However, it’s important to know that if you use an external power source, you won’t be able to tell if the parasitic draw comes from any of these hooked up accessories or electronics.

[@donmiller61]

@@classiccarmaintenance Lately with my "modern car" ('07 Acura MDX) I had a parasitic draw (well-known to dealers and many, many owners) and I became an armchair KZbin "expert" on the issues of draw and memory saving. With the investment of a $40 Digital Clamp Meter (that also has other Multimeter functions and probes) here's what seems to be the best "modern" approach IMHO (mostly from a former Acura mechanic): 1) Put the clamp meter around the ground cable to measure DC amps. No battery cable disconnection. No outside power e.g. 9V battery, another 12v battery, or jump starter, needed to maintain memory components or to hide a parasitic draw. 2) Test compatible fuses (conductive access to both poles) with a multimeter in a systematic manner without pulling the fuses to test voltage drop. If a wiring diagram is available that's even better, or just common sense from labels on the fuse box works, e.g. if the radio or wipers work - don't bother testing their fuses.

[@berndm9743]

Too bad you didn't mention that this procedure might erase all the radio station presets as well as a number of other devices as well.

[@classiccarmaintenance]

Good point! We mentioned this in a pinned comment, as our car didn't have presets. Thanks for highlighting it for others to keep in mind!

[@Playboyer670]

Will this work wirh a multimeter that only has 5A?

[@classiccarmaintenance]

If you make sure that everything in your car is switched off before testing and if the parasitic draw is below 5A, it will work just fine. Worst case, if the parasitic draw is higher than 5A, your multimeter might blow its internal fuse. Most multimeters have glass fuses, which are cheap and easy to replace, so that’s no big deal. We’ll be making a video and a post about that in the near future, by the way. If you don’t feel confident about your multimeter, you might want to check out our post about the best multimeters through the link in the description. A good one doesn’t have to be expensive. Hope that helps you out. Happy cruisin’!