llawrednav

Hey Folks,

To the point, my question: Using a multimeter in place of the battery, what should the resistance reading be between the negative and positive battery cables? (This is on a '99.)

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Background: Like many of you, I've been chasing down electrical gremlins (battery drain issues). I'm doing it systematically using the wealth of info on this forum. I've used Bill Curlee's guides to locate some guilty circuits and refurbish ground the connections. Now I'm doing a "Big 3" wiring upgrade...

While I have it apart, I'm wondering if the resistance between the battery cables will give me any additional clues regarding the health of my electrical system. Oddly, when I hook up the multimeter in place of the battery, the reading starts around 0.3 ohms resistance (supposing I have the correct range selected on the meter) then--over the course of nearly a minute--it drops to about half that before settling out. The engine is cold, so temperature shouldn't be a factor. Is there a residual charge somewhere that would cause such a thing? Bear in mind that I have fairly limited knowledge of electrical engineering.

In any case, thanks for your feedback.
- Kevin

martysauto

I'm not sure why you are doing the "test" you describe. I haver never heard of such a test. If your battery is good but goes dead after sitting a few days to a week, you need to do a parasitic draw test. It's been discussed here many times

4XLR8N

I don't think you will learn anything meaningful taking a resistance measurement as you just described. Way too many variables come into play.

If you want to measure the resistance of either cable, one at a time, that would be more meaningful. However, connections are far more likely to be introducing excessive resistance into a circuit than the cables or wires themselves.

Bill Curlee

I agree. That test will tell you nothing other than you have a normal LOAD on the BATT circuit. That would be the BCM, PCM and any other module that has a keep alive B+ (battery current applied at all times)

All those B+ loads should consume really close to 25 milliamps when the BCM goes into sleep mode.

You measure that by placing a DC Amp meter between the neg battery terminal and cable and waiting approx 10-12 min for sleep mode.

What you are having issues with and trying to track down is something that is NOT turning OFF after you shut down the car (ignition switch to OFF).

BC

llawrednav

Thanks guys. I have done the fuse-by-fuse hunt already. Fuses #5 and #6 in the foot well are responsible for most of the drain. Without them, it's pulling about 20mA. With them, it is above 100mA, #5 making up most of that excess.

I know #5 is the radio, but I've not been able to find a specific solution on here. My present thought is to either replace the head unit and/or put a manual switch in that circuit.

Thoughts?

Thanks Again,
- K

Bill Curlee

Two things are possible here. The radio has a BOSE amp and the relay that controls it can stick ON and cause that issue. The Head is actually controlled by the BCM. The BCM turns the stereo ON & OFF. There is 12VDC battery power to the head unit at all times.

Check the BOSE AMP relay first.

If the relay isn’t the issue, the BCM could be having issues turning the stereo off.

BC

Smoken1

Swap the relay with another one and see if the draw goes away

llawrednav

Wow, the Electrical Guru himself has rung in! Bill, I have been using your articles to guide many of my electrical adventures over the past decade. Thanks for all your contributions. (That is not to discredit anyone else; thanks to all of you as well.)

I'll swap that relay this evening and report back tomorrow.

- K

Smoken1

Just an FYI don't swap relays. Just replace it with another or you may end up with the same draw on another system

llawrednav

Duly noted, Smoken1. To be clear, we are talking about the #45 mini relay "Bose Speakers" in the passenger footwell, correct?

- K

Smoken1

Check your Pm's

llawrednav

The Bose relay is good. If it's a BCM issue, I may just put a manual switch in the radio circuit (440). It also might make for a convenient excuse to do a stereo upgrade...

heavymetals

You cannot get a good measurement that way.
A better way would be to record the voltage drop across the length of the cable while you are drawing a load and record the current (using a clamp type sensor).
Then you can calculate the resistance of the cable when under a load.
Or you get yourself a 4 wire resistance meter (milliohm meter)

llawrednav

Thanks, heavymetals. I have been educating myself on these things and found that I should be doing what you described. As you might have seen, this thread has now evolved into a more specific issue with amp leakage in the radio circuit. Hopefully I'll discover something useful to report back to the forum.

Cheers,
- K

llawrednav

Old thread, but I actually only just discovered the root cause of my excessive battery drain while doing some sound deadening...

The original owner had installed a LoJack transmitter under the carpet beside the driver's seat. It was vampire-spliced into a radio power line that runs through the center console. Presumably, once the LoJack battery had died, it was intermittently pulling power to send tracking data.

This info will probably be of little use to anyone else, but I didn't want to leave the thread dead-ended forever.

Cheers,
- K




LoJack device and its battery pack (source of my battery drain).

Bill Curlee

Thank you very much for the interesting update.. Looked like HACK JOB!

Good work!