Auto Electric Troubleshooting 101 Question

I need to determine if something is pulling too much current when the car is shut down causing the battery to go damn near dead in one week's time of no use.


The "Southwire Autoranging Multimeter" I have has a setting labelled mA. Is that the milliamps setting to measure current draw?


The leads get connected to the disconnected neg. cable and the neg. post on the battery. I did get a 315 Ma reading and understand less than 100 milliamps is desirable.

check for draw at the fuse panel

philski o'flood said:

check for draw at the fuse panel

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I recon I can do that, thanks. What I was told was to connect the multimeter to the battery as I described and start pulling fuses until the draw dropped.

Aftermarket stereo?

lummert said:

Aftermarket stereo?

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Nope.

300 milliamps is way too much. I have been trained that around 7 milliamps is acceptable on old cars. Modern cars with keep alive memory (KAM) modules, 20 milliamps is more acceptable.

300 milliamps is a third of one amp. Pull fuses one at a time until that draw is close to zero.

One recent drain I found was a telephone unit on an old Mercedes; I unplugged the unit. The other was power seatbelts on a 1990 civic.

Here is the catch, on modern cars with alarms and lights that flash, I fried my meter trying to connect it. One can connect a jumper wire so the initial load doesn't go thru the meter, the. Pull the jumper.


Orrr get an amp clamp and leave the battery cable connected!!!

Good luck. Commonly it's wiring for the locks in the doors.


Once you have located the circuit with the drain, start unplugging components again until the drain goes away.

Zach is right, run a jumper wire, pull the cable from the post, then connect your DVOM, so you don't have the initial load. Also keep in mind you have some modules that will go to sleep. Need more info on what the car is to know if that's an issue.

35ma or less has been a common industry standard over many makes for some time, even on the newer stuff.

Pulling the fuses is indeed an easy way to tell what's going on. Could be something like the power antenna with a relay that's stuck on as well, or possibly even a connection that has some corrosion between a power circuit and load/ground circuit.

In addition, tell us what kind of car you're working on. The generic advice is great, but if you happen to be working on a Volvo, many of us already have identified the usual suspects, according to model and year.