Deserion

I only discovered it by happenstance in my case. It had been about two days since the car was last started to move it back into the garage, and the window relay case was warm to the touch (non-contact thermometer was showing ~103 degrees). After I removed the case I reinserted the relay and cycled through car on-off-key out-door open and checked the relay contacts. Prior to cleaning the relay would stay closed even though the windows were inop. Once I cleaned it, the relay would open after a door had been opened in the same cycle as before. Thermometer shows the case at the same temperature as other relays (~86 degrees while in my garage). Testing for voltage drop showed no circuits drawing power, thankfully ruled out control modules and CCU fan.

From what I recall the windows are on a time-delay when the key is removed and door(s) unopened. Would need to dig into the schema on that one though.

Kappi2907

Nope, finding the device that's causing the battery to run down. If you see the leakage current disappaer on your multimeter after removing a specific fuse, you have check devices (e.g light in the frunk).
Very easy way to find simple electric problems.

Stephen Koch

I dont think he has a current drain as such. If the car thinks the door is open even when it is closed and locked so it is keeping the car powered up including window switches. In my car when this happens takes about 0.6 Amps, if the car is properly off it only takes about 0.04 amps. I dont think this is a drain as such, the issue is that the car is keeping everything powered up when it shouldnt. It is supposed to only do this for a short period after the doors are closed and the car is locked. The current drain is going to be window switches and anything else the car is keeping powered up, however the problem is why does the car keep everything powered up.

Matt if your car has the same issue as mine which in my case it thinks the hood is open when it isnt then there is a white male to female connector in the top left corner (bare in mind my car is RHD) by the fuse box area but to the left of this where the hinge is for the hood. I have unclipped mine so i’ve disconnected the switch from the hood and the issue stopped. It is very easy to do and i would say worth a try. If you cant find it i can post a pic when i get home.

Matt Andrews

Thanks Stephen. I think you are referring to the switch that controls the boot light. Pretty sure my car does not have one. But let me know if it isn’t in this area:

Stephen Koch

Yes that is the right place just to left of the hinge so looks like that isnt he cause for you.

Earlydays

It could be your alarm CU, which is behind the left hinge and to the left, attached vertically.

Matt Andrews

left hood hinge? or door hinge? How would I test it? pop the hood while the alarm is armed and see if it goes off? I wouldn't mind disabling it. There is no alarm need on this car...

JohnK964

My MY 91 C2 Coupe has the alarm CCU under the right hand seat not sure when the change from by the hinge was made

Deserion

PET shows that the new module is 1991+.

The alarm box is in the right-hand-side hood hinge but only into 1990. Yours is under the right-hand-side seat and is a more complex unit.

Silvertarga

check your drivers door light switch, ease and cheap to replace

Matt Andrews

So I did something more basic than any of the tests suggested. I just pulled the power door lock relay under the hood. Left it for a few days, and the battery still has a charge. Sounds obvious, but this means the relay is bad, right? Or could there be some other wiring issue that is dormant with the relay unplugged, and could still be there if I replace the relay?

Matt Andrews

HA! spoke too soon. Went back 3 days later and it was dead as a doornail...

cobalt

So your car has a micro switch as part of the hood latch and the pin switch was only used on the earlier MY cars. If you leave the hood open it will leave the light on and not allow the car to go into rest mode and discharge the battery. Did you ever load test the battery. You could have a dead cell.

One thing you can try is remove the battery and drop it a foot or so from the floor away from the car. It has helped me with several batteries and they came back to life. I would load test it and you should consider investing in a quality charger. Some of the higher end chargers have reconditioning modes that will help as well. Although check that you don't have any draws in the system. Or you can try one of the Antigravity batteries and report back

Matt Andrews

Im Away from the car for the next 5 days, but need to look closer when I get home. This car was not equipped with a front boot light, so I’m not sure it has the micro switch. Do you know for sure if the euro RS had them?

cobalt

That is a good question. I am getting my cars confused US Cup vs RS. Hard to say the PET shows the RS having the same wiring harness as the Turbo Look so I am assuming it should. Although it doesn't help if something is omitted from the RS/Cup cars. I am curious to know if it does or not. In either case does it have an alarm? If it does the alarm also uses the switch whether it has a light or not. It does show only one front latch for those years so again I am assuming it has the micro switch. Whether it is plugged into the harness or not you would need to let us know.

I am curious the RS shows a different part number for the rear engine lid. Is it aluminum? If not I am not sure why it would have a different part number.