Electrical short draining battery need advice.

Adidas · 07-30-2007, 01:26 PM

I have a 1993 964 Cabriolet and have an electrical short somewhere that drains the battery. Is there an easy way to find this problem. In the past I usually disconnect the battery ground cable and remove one fuse at a time and look for a spark when reconnecting the cable which sometimes has led me to the problem. Are there other ways to diagnose this or could this be a bad relay as well? Thanks in advance Bill

07-31-2007, 08:15 AM

Just went through this... Put an ampmeter in line with the battery and started pulling fuses. That will point you to the circuit(s) that are pulling to much current. With everything off, you should have under 40 mA draw... In my case there was a short in the truck light and the rear spoiler controller was drawing double the normal amount....

my $0.02

-CKKrause

Adidas · 08-17-2007, 08:32 AM

I took Rob's advice and connected a 12 volt test light between the negative pole of the battery and cable and the light came on and actually flickered.. I unplugged all fuses and relays one a a time in the main relay board with no success. With the test light still connected and on. I then heard a ticking noise and took out the passenger seat and found this large relay or control unit ticking like a clock and unplugged the 2 multi-pin connectors and the light went out. I've posted a picture below. This appears to be the central locking relay part# 928 618 260 01. It appears that this is draining the battery The car would not crank with this relay unplugged. Can this one be repaired or bypassed? Any advice appreciated. Thanks

DW SD · 08-17-2007, 10:34 AM

Maybe try disconnecting the central locking switches and see if one is continuing to send a signal to the relay? I would suspect that relay is not computer controlled, but it could be, which could be why the car won't fire.

Does it have a factory built in alarm? If so, maybe there is some logic related to the locking relay which is tied in to kill the computer if the relay is diabled.

There is some chance the relay is bad, too?

Your picture was not attached, which could help some other troubleshooter.

Can you find a wiring diagram for it? If so, we can probably take a better guess at what is wrong.

Doug

Tom W · Tom W's Garage

There is supposed to be some current draw when your car is off - the clock and the security system are two of them. You can't do the testing with a simple light, you need a digital mutimeter that can measure at amps (they typically can do 10 amps). This allows you to distinguish between the stuff that's drawing a little current or a lot.

In my case, I battled the battery drain for over a year. I had a relay (wipers, I think) that had an intermitent problem. Whenever I check the current draw it was fine (<80 mA) but at times it would drain down to nothing. As my time was limited, I cheated and ignored the problem for most of the year and simply kept the car hooked up to a trickle charger.

Don Settergren · Don Settergren's Garage

I remember reading a thread where the current draw was found to be the bonnet\trunk light. It's the first thing well disable so we can test the rest of the car with the lid open...