94 850 Turbo Parasitic Battery Drain - Very Strange Phenomenon

budoboy · Post by **budoboy** » 27 Feb 2021, 18:18

I recently bought a 1994 850 Turbo and noticed shortly after buying it that it has a parasitic battery drain. The car can't sit for more than two or three days before the battery is too low to turn the engine over. From my measurements, I see about a 350mA draw on fuse 15. I have checked usual suspects on fuse 15 (radio, glovebox light, remote locks, vanity lights, courtesy lights, etc) and still haven't been able to figure out what is using so much amperage. In fact, I think the person who owned the car before me went through a similar investigation of phantom power draw since every thing that I have checked has had loose or broken plastic pieces indicating that someone had taken things apart before.

While I'm still trying to find what is causing the drain, I came across something very strange (at least it seems strange to me). I had taken fuse 15 out so no current should have been flowing through the circuit for the central courtesy lights by the rear view mirror. With the car off, and the doors closed (and fuse 15 still out), I measured the voltage coming to the harness on the light fixture. The voltage measured 9.9 volts. I know that line is supposed to always be "hot" since you can turn on the over head lights even when the car is off, but with the fuse removed, it shouldn't be allowing any flow of electricity to happen (every other thing on fuse 15 is not getting power as far as I can tell). When I put the fuse back in, the voltage at that harness jumps back up to the nominal battery voltage as expected(12.8 volts). Does anyone have any idea why I would be able to measure 9.9 volts to the harness with the fuse removed? Could this indicate what is actually causing the power drain?

Any input would be greatly appreciated.

Cheers,

Bryan

Post by **ZionXIX** » 27 Feb 2021, 18:44

I would pull fuse 15 and then watch the 9.9volts while pulling the other fuses 1 at a time until it goes to 0

Post by **abscate** » 27 Feb 2021, 19:32

The overhead lights are a complex circuit with multiple power feeds and pull downs through the 2/76 lock controller. It won’t troubleshoot like a simple 12v supply, switch, load, ground approach.

You can get a sense of this here

viewtopic.php?f=1&t=88623&hilit=2%2F76+lock+controller

Post by **misha** » 28 Feb 2021, 02:10

Aftermarket alarm system,aftermarket radio or you simply have a short somewhere in the circuit.

Post by **scot850** » 28 Feb 2021, 10:48

is it a wagon or sedan? I missed it if you said.

Have you removed the glove box light bulb? Check it is not sticking on. Common issue. You can check easily but sticking your phone in the glove box in video mode and seeing if the light stays on when closed.

Reason for the sedan/wagon is that both are prone to cable breaks in the trunk lid wiring where it enters the trunk and goes to the lid, and the wagon where the wires enter the tailgate at the hinge on LH side. Could be getting a short in either. You can also get similar issues in the door harnesses. At least with the door harnesses you can remove each in turn and see if the draw goes away.

Neil.

budoboy · Post by **budoboy** » 28 Feb 2021, 19:10

Thanks for all the replies.

I have a sedan. Sorry I didn't mention it before.

There is definitely a draw on fuse 15, but there also seems to be a draw on fuse 6(central locking system) with the car off.

For my troubleshooting, I have removed the glove box light bulb, overhead light fixture, unplugged the factory radio, and unplugged the remote locks system module. I did some more troubleshooting today by unhooking the front door harnesses but the draw remained. I will see if I can test the trunk soon.

Thanks to abscate for the link to that schematic. I had no idea there were circuits so inbred in the car. I am not an electrical engineer/technician so I don't fully understand the whole schematic. I tried Zionxix's idea but the overhead light voltage didn't change when I removed every other fuse. The only time it did change is when I would open the door latch, then the voltage would drop to 0 on the overhead light circuit. After looking at the schematic, I am not surprised closing the circuit to the door light would do something to the overhead light.

I think maybe one of the larger fuses or relays could be causing part of the issue as well.

I think I need to get a much better multimeter. The cheapo multimeter I have doesn't have the resolution that I would like and could be causing more confusion than clarity.

Regards.

Post by **RickHaleParker** » 28 Feb 2021, 20:35

budoboy wrote: ↑27 Feb 2021, 18:18 Does anyone have any idea why I would be able to measure 9.9 volts to the harness with the fuse removed?

It would help if you tell which two electrical points you are measuring across.

rsmigel · Post by **rsmigel** » 21 Nov 2021, 11:55

What would you expect on a properly running ‘94 turbo wagon? I’m measuring 10 mA across the negative terminal with the ignition off.

Post by **scot850** » 21 Nov 2021, 13:38

If you remove the -ve battery cable, and then connect a electrical tester across the negative terminal to the -ve battery connector, you will see the drain. If that is what you are doing, 10mA is a normal condition. On later P80's up to 50mA is ok.

Neil.

fnord · Post by **fnord** » 21 Nov 2021, 18:32

I have a similar drain on my '95 850 (non-turbo). I pulled fuse 5 (30a, blower speed 4) and the drain ceased, but when I re-plugged the fuse, I heard a short whirring sound in the area of the compressor/power steering pump. I only have the 4th speed on my AC because I need a new resistor for speeds 1-3. What causes the whirring?
I also removed fuse 15 (courtesy lights) because the footlight would come on when I hit a bump, or it would have a problem shutting off when I closed the door. On most older cars there was a button in the door jamb that controlled the interior lights, but I can't find any sort of switch or sensor that does the same for the 850.