How do I find a parasitic power draw?

extremetrek · Jun 17, 2005

Hello again,

As some of you are aware, I have been suffering an electrical issue with my battery which causes my car to not start, or hesitate to start at times. Generally this occurs while using accesories if the car is off even for 30 seconds. I took the car down to the place the battery was purchased from and I was told that I had a parasitic power draw on the battery, which is why the battery operates almost completely discharged. Ok, so I don't want to take my car to the mechanic unless I have to, so I am looking for anyone who has had a similar issue and found the source so that I can check some simple stuff before shelling out the dough for someone else to do it. Here are some symptoms:

- When accesories are on and car is not, even for seconds, the car will not start at first, then after a couple minutes it hesitates and starts.

- I have a fuse which operates the cigarette lighter and power seat that continually blows or fails to operate, which can sometimes be fixed by pounding on the fuse box under the hood.

- I have a strange new pinging which I have been advised could be due to a fuel pump problem.

I think that ought to be enough info to start. I check this regularly so feel free to ask questions to help me diagnose this thing. Thanks!

EDIT: I think I solved it, the power seat switch was stuck in the down position which was probably the source of the draw, that or something else on that circuit.

mo_dingo · Jun 17, 2005

Hey, prescott, I have family there.

Problem #1. By "accessories", you mean the air conditioning only, right? because that is the only acc. you have direct control over. Please explain of not. You should turn off the a/c BEFORE you start the car, always.

Anywho, start with the basics. Do you have a DVM. You need to check the system to see if you have some sort of power draw w/ everything off.

Disconnect the negative cable on the battery and set it aside.. Hook one lead of the DVM to the battery post, and hook the other to the negative cable (still disconnected). Set the DVM to Current (20A setting for now), aka A or amps.

See how many amps the car is sucking from the battery.

Leave that hooked up, have someone watch it, and start disconnecting fuses, 1 by 1. After you disconnect one, check the DVM and see if the amp load has changed. Repeat for each fuse until they are all disconnected.

If the load is still there, then you need to start with the main fuses inside the engine compartment. Repeat the same procedure for those.

Once you find which fuse is drawing the current, use a wiring diagram, and backprobe each circuit that uses that fuse and see which one is drawing current.

Obviously you have a short at the fuse for the lighter. Disconnect EVERYTHING that uses that fuse, install the fuse, makd sure it doesn't blow, and one by one, connect something and see if the fuse blows (continuity test w/ DVM is easiest test). If it doesn't, disconnect it and try the next one on the list. Keep trying until find the one that blows the fuse. Then test the wiring and see which wire is shorted out. Then trace that wire back to it's origin. You should find the wire is pulled out, insulation is stripped and wire is grounded out.

If you can't see a short, cut the wire near the part it's connected to, and see if the wire is still shorted. If it is, it's definately the wire. If not, the item it was connected to has internally shorted out and needs to be replaced.
Scott

HISSIN50 · Jun 17, 2005

as an aside, make sure no change fell into the cig lighter receptacle.

Good luck hunting shorts.

extremetrek · Jun 17, 2005

I suppose accesories was the wrong word, I really mean anything at all, lights, radio, courtesy lights with doors open, engine bay light, trunk light, anything will kill it.

As I said, I have narrowed it down using the method you gave me to that single fuse which controls the seat and cig lighter. Although looking at it now, I think that i just had the power seat control in the down position and that the drain really isn't as bad as I thought...though the battery is dead and there probably is a bit of a short in the cig lighter...but we'll see, ill look for it in the morning. Thanks for the info though, well appreciated!

HISSIN50 · Jun 18, 2005

Yeah, as Scott mentioned, once you narrow it down to one fuse, you can start disconnecting accessories in that circuit (e.g. disconnect the cig lighter connector and see if the meter drops).

The seat motor uses a relative ton of juice. You can disconnect its connector(s) under the seat to see if that helps.

Good luck.

BPA · Jun 18, 2005

and im sure you know this but it happens to all of us from time to time, make sure you change the volt meter positve cable over to the fused amp corisponding conector. Hate it when i blow fuses on the volt meter .. max alowable draw is .05 Amps on most modern cars

How do I find a parasitic power draw?

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