My brother's SDL has suddenly started draining batteries and eating alternators. He put a new alternator on a couple weeks ago when it stopped charging (bad diodes), but the battery kept going flat, so we swapped in a known good one. Still went down, put another alternator on because the new one stopped charging.

I was messing about with it last night, isolated the current draw with the key off to fuses #2 and #15. Alternator (last night, anyway) was putting out 14 V, so that is OK at least for now. Key off drain, no lights on, is 0.74A.

Problem is I cannot find what's sucking juice on fuse #15! Lock pump works, antenna motor isn't the culprit, it's not the lamps that run off that fuse, there is no seat belt positioner, what's left?

I've not heard anything today, so I guess it's fine with fuse 15 pulled.

Only other strange thing is that the interior light stays on after closing the door. Not the normal 15 sec or so, but indefinitely. Turned that off, but is that relay on fuse 15, and where is it?

I don't have a manual for this car, can anyone help?

Thanks!

Peter

__________________
1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!

Peter,
When my interior light stayed on (in my 124, and I also do not have an SDL manual) it was a fuse (#13 I think) that was blown but, as you know can happen, appeared good visually. So that might be a separate issue?

I wish I could offer you more than this to repay your helping me in the past
Best of luck.
Marty

__________________
-Marty

1986 300E 220,000 miles+ transmission impossible
(Now waiting under a bridge in order to become one)

Reading your M103 duty cycle:
http://www.peachparts.com/shopforum/showpost.php?p=831799&postcount=13
http://www.peachparts.com/shopforum/showpost.php?p=831807&postcount=14

Fred:

I have a gas '91 300-SEL W126 car - not diesel - but I suspect that circuit might be pretty much the same in any 126 car.

I just pulled the fuse cover off of it and will list off everything tied to fuse 15:

- roof light rear
- trunk light
- safety belt handover arm
- switch over valve seat back arrester
- central locking system
- door lights
- reading lamps/rear compartment
- aut. antenna
- control unit seat adjustment memory

To get an idea what happens to the 126 battery when the doors are opened(interior lights come on), hook up your VOM for an open circuit volt. test, then have someone open the door. Watch the VOM. WOW!

Trunk lights seem to come up a lot at this site. Don't know if that's just diyer reiteration or if it's actually a common problem on 126 cars.

If you suspect the trunk light and can't find a volunteer to crawl inside to see if it's on when the lid is closed, place a cam-coder inside, tilted so that's it's pointing at the light. Close the trunk lid, wait a bit, open it up; then go play the tape.

__________________
Mike Murrell
1991 300-SEL - Model 126
M103 - SOHC
"Fräulein"

Suspects that have both been at fault at one time or another in the past relating to battery drain, at least for me:

1)warning module next to cruise amp.(fried relay points) thru fuse #2.

2)anti-theft system module under passenger footwell (POS generally) thru fuse #15.

FWIW

__________________
The Golden Rule

1984 300SD (bought new, sold it in 1988, bought it back 13 yrs. later)

Hi,

I am having the exact same problem with the exact same fuse. My vehicle is an 87 560 SEL. I am right in the middle of figuring it out and assume I dont have near the Benz mechanical experience you do.

I will give you some of my info in the hope it helps.

I believe this all started when I charged my battery with a charger, had car positive cable hooked to the battery and used too much voltage to jump start it (200 amp quick start). I seem to have blown out a number of electronic boards in a number of parts.

With # 15 fuse pulled battery does not drain.

I noted that although my central lock pump worked, it seemed to stay on slightly. I did not hear it at first and can only assume it did so intermittantly or was tool low for me to hear. When I put it in a quieter area I noticed it. I took it out and it smelled wrong (burned) so I disconnected it.

It seems that this has slowered or stopped the drain but I am not sure yet because I want to let the car sit for a few days to see if this has fixed my problem. The drain was so slight that it would take 3-5 days before depleting battery enough not to start.

I guess a good idea might be to disconnect all known connected items, even though they seem to be working fine, and wait a X days. If battery does not drain, obviously wiring and anything else connected is all ok. Then reconnect individual items one at a time and wait a few days between each. Continue until you find the culprit. This may seem long and a hassle but I have been dealing with this problem for awhile - so if you know or find a better way PLEASE post it so I can get this headache over with.

Best Regards,

Lance