Electrical Problems- W124
 

Hello All,
I was hoping to get a little help with some electrical problems I'm dealing with on an 87 TD wagon. A charged battery goes dead within 24 hours. I removed all the fuses with no change. I narrowed it down to a red, cotton wire that starts at a junction terminal positioned in front of the battery and appears to go behind the fuse box.

Other issues, maybe they are related: cruise control not functioning, power seats only work with doors open, half the interior lights not working properly.

TIA!

When you say you narrowed it down, what do you mean exactly? I am assuming that the battery is going dead without having driven the car at all - so it's not an alternator problem. In that case you have a parasitic drain. Trying to find your parasitic drain can be as easy as installing an ammeter in series with one of your battery cables. If you read high (over 25-50 milliamps) then something is drawing too much current. Start pulling fuses until you see your milliamps drop. Of course, when i say "can be as easy as," I mean could possibly have the potential to be easy - seems I always end up pulling my hair out (if I had any) over these things. The other potential problem is that all of the electrical components that now require power when the ignition is off causing problems. Attached is a PDF that I have found helpful in the past. Good luck!

Red Cotton Insulated Wire...In a Mercedes?
 

That may be your culprit...disconnect it and put a test light "In Series" with it
...Does the light light up?
See if you can find what sort of "AfterMarket" Device it's Powering.

Are you saying with ALL the fuses pulled the battery still drains down? Might be
a bad component (Diode?) in the Alternator.[It's non fused,so it always has
access to the battery.]

Tankowner,
Thanks for responding. When I say "narrow it down", I mean that I ran a volt meter between the battery 's negative post and the negative cable. With all the fuses taken out, there was still a 12 volt loss.

I did a test with the amp meter with all the fuses in, as you suggested, and it would show over 5 amps for a few seconds and then drop to .16 amps.

Compress Ignite - OK, so it may not be exactly cotton :) but it is some sort of fabric material; it looks like it's factory. When you unhook it, there's no power anywhere. It seems like it would be powering the fuses. It's pretty heavy guage wire. When I connect it or disconnect, I get sparks.

Thanks to both of you for all your help.

If you get sparks, then something on that wire is drawing current. That is what is causing the battery to go flat. You have to trace that wire, see where it goes and what is connected to it. It can be a slow process but there really is no other way.

Convenience relay (holds the interior lights on after you close the door, flashes the seatbelt sign, etc.). When they fail, they draw power and will run the battery flat with no other signs. You at least have the other symptoms.

Peter