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When you hook up the multimeter between the negative battery terminal and the black battery cable, it functions as a bridge allowing power through. This, however, is limited by your multimeters' internal fuse(s). If you turn on too much electrical stuff and draw too much power, its fuse(s) will blow and you'll have to replace them.

That’s correct, the multimeter leads form a bridge between the negative battery cable and negative battery post allowing power through. Any draw below 50 milliamps is normal and should not drain a healthy battery. If your battery keeps dying without a parasitic draw, either your alternator isn’t charging properly anymore causing your battery to drain while driving, or your battery itself is bad and can’t hold its voltage anymore. We have videos about how to test both your alternator and your battery, so make sure to check them out, it’s super easy! How to test your alternator with a multimeter: kzbin.info/www/bejne/bZKqg6asZdijgcU How to test your car battery: kzbin.info/www/bejne/fZaofqWGhK5jrq8

@@classiccarmaintenance Ended up using a clamp meter from a neighbor that worked SUPER well to see the draw real time without worrying about the cables. Was able to pull fuses til I found the right one. Ended up being a SJB, which is not the best answer but an answer.

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Switching the positive and negative test leads 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.

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When you hook up the multimeter between the negative battery terminal and the black battery cable, it functions as a bridge allowing power through. This, however, is limited by your multimeters' internal fuse(s). If you turn on too much electrical stuff and draw too much power, its fuse(s) will blow and you'll have to replace them.

Now you know which circuit the parasitic draw is located on, you can start to narrow it down further. You want to check the circuit for damaged wiring, or an electric device/component that might be faulty. Once you’ve determined by elimination what is causing the parasitic draw on that fused circuit, you now know what needs to be repaired or replaced to eliminate the parasitic draw.

If your vehicle has 2 batteries that are set up in a parallel or series configuration, you only need to unhook the black (negative) cable that runs to the ground/chassis and place your multimeter in between that negative battery terminal and black (negative) battery cable, without disconnecting the battery cables that connect both batteries. If you have 1 battery for your engine and a separate one for your auxiliary power and accessories, you need to test the batteries one by one. First do the test with 1 battery and its corresponding fuses, and then the other with its fuses.

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As clearly shown in our video, the CTEK clamps didn’t snap off when moving the connectors, even with our positive battery cable only having barely enough play to move to the side. As long as you use a quality power supply with decent clamps and you’re careful when disconnecting the battery cables, you’ll be fine. As for the thumbnail of our video: the picture was taken during the making of the video, but from a different angle. When you watch our video closely, you can see that we showed every step from start to finish and added the clamps before the battery cables were removed, not after.

Yes, this works for any vehicle with a battery and fuses.

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There’s something wrong if your multimeter shows 0 amps in the (DC) amps setting with the negative (black) battery cable disconnected from the battery post, and the tester leads between the negative battery terminal and the black battery cable. A 0 reading means there’s something wrong with your multimeter or the positive battery connection as there will always be a tiny amp draw somewhere because a cars’ electric wiring is never perfect. Normal readings should be anywhere between a few milliamps and 50 milliamps. When you test for voltage between the battery terminals with your multimeter in the DC voltage setting, a normal value would be between 12.4V and 14V (freshly disconnected from a charger).

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You’re welcome! There’s no such thing as a parasitic draw from a “faulty” ground. A faulty ground means there is a bad connection between the electrical component (e.g. radio, lamp, horn,…) and the ground (meaning any bare metal part of the car or negative wire). As a result, the component will malfunction or not function at all. This however does not cause a parasitic draw. A parasitic draw results from the (positive) wiring contacting any metal parts or negative ground wiring, an internal fault in a device or a device or lamp that stays on after the contact is switched off. That’s why you have to test fuse by fuse to determine where the draw is situated. Once you’ve pin-pointed the problem, you can fix it. This however can sometimes be hard to find if a (positive) cables’ insulation is damaged and it contacts the ground (any metal part or negative wire) somewhere behind the dashboard for example. Worst case scenario, while testing for a damaged cable, the cable slightly moves and loses its connection with the ground, temporarily making the parasitic draw go away and undetectable. In this worst case scenario, a visual inspection of all cable insulation is needed. Any damaged or melted wiring should be replaced.

@ thank you very much for taking time to explain in detail for me. I truly appreciate your help. But if there is a loose or faulty ground from the car chassis what other issues might result??? Could something like that cause the battery to draw down over night ?? Or is any battery draw going to be caused by issues with positive wires being grounded like you describe or a component being faulty or switch staying open??? Last question if I may please ?? If a relay is faulty (Burnt) or shorted out could that faulty relay cause a parasitic draw ?? Thank you so very much Mark Ward

If a ground is loose or faulty, the affected electrical component will either not work at all (e.g. ground disconnected and the component does not receive power) or not work properly (e.g. a corroded headlight connection that only delivers 8V while the component needs 12V, causing one of the headlights not to shine at full brightness). A loose or faulty ground however, cannot cause a power draw and will not drain your battery. A parasitic draw results from the (positive) wiring contacting any metal parts or negative ground wiring, an internal fault in a device or a device or lamp that stays on after the contact is switched off. A relay can also cause a parasitic draw either at the primary or secondary circuit. If there’s a short circuit in the primary circuit, this can generate heat which causes a small parasitic draw that drains the car battery. The secondary circuit, a contact that allows power to go to a powerful electrical component when it’s closed (e.g. to the headlights) can also cause a parasitic drain when it shorts internally. This can cause 3 different scenarios that will cause your battery to drain: the component stays on permanently, it only functions partially or it will not work at all. If the component doesn’t work at all when it’s switched on, with a faulty secondary circuit in your relay, it can still generate enough internal heat in the relay to get a parasitic draw. While the first two scenarios are easy to diagnose (always on or not functioning properly) the last scenario is the least likely but often overlooked because one assumes that a component that is not working does not draw power. While the component is not drawing power, the internal secondary circuit of the relay can be causing a parasitic draw. So in short: Sure, a relay can cause a parasitic draw, and the easiest way to find out is to test the fuses in your fuse box(es) like we showed in our video. Then you’ll know where to look.

If you changed the alternator and battery multiple times, I’m going to assume your issue is that your battery keeps dying which is usually caused by a parasitic draw. You should start by following the instructions in the video to determine if you have a parasitic draw and where it is located. Once you know where to look, you can start looking for a solution. It might be as simple as a glove box light or trunk light that does not turn off when closed! The simplest way to find out is to do the test as shown in our video.

It’s a foolproof test though. If the parasitic draw is located on the fuse that powers the radio, it means that either the radio itself or the wiring to the radio is the problem. If disconnecting or replacing the radio does not solve the problem, the issue is probably located somewhere in the wiring that connects the fuse to the radio, or in the fuse box itself.

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The reason why we recommend using a 12V power supply hooked directly to the battery cables is because the power runs through the fuse box, meaning all your cars’ sensitive components are protected from power surges and overload. Although we don’t recommend any specific product, we did link to the professional 12V charger and power supply we used in the video because we know it works great, but you can use any stabilized 12V power supply to do this of course.

I think that OBD-based power supplies can fail or jack up the vehicle’s electronics. Connecting a 12.6 V power supply directly to the cables that attach to the battery is fail safe.

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No, this probably won’t work because it seems like lots of different electronics start acting weird randomly, and it’s unlikely that all these different circuits are malfunctioning because of the rain. It rather sounds like your cars’ computer, which controls all these electronics, is short-circuiting or flipping because of false input or overload. This may be caused by your car computers’ connector plugs or one or more sensors not being waterproof and causing short circuits when they get wet. You could first try to clean the connector plugs with contact cleaner and put dielectric grease in the contacts to keep the water out and prevent further short circuits and oxidation. As a consequence of disconnecting your cars’ computer(s), your saved computer settings might be lost and might need to be reset.

We've put a link to the 12V power supply we've used in the description under the video so you can easily find it.

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No, the fuse itself isn’t the problem. Pulling the fuses is just a way to easily locate on which circuit the parasitic draw is located. If you pull the fuse that protects the radio only, for example, and the parasitic draw disappears, you know the radio or its wiring is causing a parasitic draw. The radio might not be switched off, as shown in our simulation, or there might be a damaged wire, or the radio itself might be faulty. Once you’ve determined by elimination which part(s) is(are) causing a parasitic draw, you know what needs to be repaired or replaced.

@ makes sense. So I know it’s my 12v plug. If I leave my stuff plugged it my car dies in about an hour and a half. Not fully just not enough to start. This just started happening recently so would the whole 12v unit need replaced somehow?

When you leave electronics plugged into your cars' 12V plug, and it’s wired to be “hot at all times”, these electronics will draw power from your cars' battery and drain it even with your contact turned off, which is normal. If your car battery doesn’t drain when nothing is plugged in to your 12V plug, then there’s nothing wrong with your 12V plug. However, if unplugging the electronics from your cars' 12V plug does not fix the issue, you might need to repair or replace the 12V unit or sort its wiring.

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Yes, if you have a spare 12V battery laying around, you can hook it up to the car's battery cables with jumper cables for example, disconnect the old battery and install a new one. It's crucial though that the spare battery remains connected untill the new battery is hooked up to the battery cables.

@@classiccarmaintenance awesome, thanks. It worked out well.

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You sure can! This will speed up the process of finding the right fuse(s) as you don't need to run back and forth to view your multimeters' readings. But watch out: you mentioned connecting the multimeter between the positive (red) terminal and the disconnected negative (black) cable, which is incorrect. You need to connect the multimeter to the disconnected negative (black) battery cable with one probe and to the negative (black) battery terminal with the other probe, otherwise the test won't work.

@@classiccarmaintenance Thanks for the help. I should pay more attention😀

You're good, that's perfectly normal for modern vehicles. The parasitic draw of 140 milliamps you measured in the beginning is because the dome light was still on and because the computer was still running in the background. Once the dome light goes out and the electronics go to sleep (the relay that clicks) you have a draw of 10 milliamps which is well below the acceptable 50 milliamps. That's why we said in the video that with modern cars you might have to wait half an hour or longer to perform this test as the cars' computer needs to go to sleep first.

@classiccarmaintenance Thank you so much, that really eased my mind. You are very helpful! I hope you get tenfolds of followers and subscribers!

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No, the only safe way to disconnect your car battery without losing your settings is to hook your cars’ battery cables or OBDII-port to a battery charger with a dedicated 12 volt “supply mode” or to a secondary 12 volt battery before disconnecting your car battery.

@@classiccarmaintenance your awesome, thank you for your wisdom.

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To test for parasitic draw you need to turn the key to the off-position and make sure nothing is drawing power. In our video however, because we did not have an actual parasitic draw, we simulated a parasitic draw by turning the key to the accessory position. This turns on the radio which draws power, and shows up on our multimeter as a parasitic draw.

Your measurement of 0.070 (70 milliamps) is above the accepted 0.050 (50 milliamps), which means you have a small parasitic draw. You now need to locate the fuse box and start pulling the fuses one by one to see on which fuse your parasitic draw is located, as shown in our video. Once you know on which fuse the parasitic draw is located, by further elimination you can now determine which wiring or electronics that are powered by this fuse is (are) causing the parasitic draw.