weird electical system problem with 1993 850

[BitHead]

I've been reading here anonymously for a while, but I've found something weird that someone here might help with, so this is my first post. I guess that on this forum, this may not qualify as weird, but I haven't seen symptoms like this before.

I have 1993 850 GLT with 145,000 miles on it, and I've had problems with the battery discharging. It would take a charge, but if I left it in my garage for a few days, it wouldn't start or barely turn over with typical low battery behavior. I'd charge it up again, run it around on weekends, and it would be fine for a few more days. I checked for interior and trunk lights left on, etc., and nothing like that was going on.

I replaced the battery last winter, and had it checked again a few weeks ago. I had a local garage check the alternator, and that was good and the wiring between battery and alternator was good. They also couldn't reproduce the behavior I saw while they had the car at the garage.

I had them look at it again more closely today, and this time they noticed that there was a drain on the battery when the engine was off, but the car wasn't locked with the key fob. I had always assumed that the alarm system would cause some drain, and never locked it in my garage, but there you go.

I didn't want to pay for a fishing expedition, and the simple workaround seems to be to just lock the car all the time. But if there's something reasonable I could do to fix this, I'd like to know about it.

So what would cause a significant drain when the car is unlocked but NOT when it's locked? Some kind of bad switch in a door, maybe? Has anyone else seen something like this?

thanks for your help,

Paul

[hethr68]

If you have a multimeter, one of the best ways to isolate the circuit that's causing the draw is to hook an ammeter in series with the battery (on the milliamp scale) under the condition that causes the draw and pull fuses, one at a time, to isolate the circuit. In your case you'd probably start with the fuses associated with the doors.

Anyway, if you have an ammeter in line with the battery on the milliamp setting - don't open your car door (because of the interior lights) or turn anything on in the car, such as the headlights, you'll blow the fuse in your meter.

Find the circuit with the high draw and you've at least isolated it a bit. From there you could work within the circuit with a similar principle to find out what's causing the draw. Or maybe this is all too much work and you could just keep it on the alarm.

[BitHead]

OK, thanks. I'll give that a try this weekend and see what I can find.

Paul