W140 93 300SD electrical drain

[sixto]

[moderator, this thread is cross-posted in Diesel discussion]

I drove the SD on Monday and everything was fine. I tried to start it on Wednesday and the battery was flat. No remote keyless entry, no dome lights, nothing. I hooked up a fresh battery but before hooking up the ground cable I checked current draw - 3.25 amps! I pulled all the fuses in the engine bay fuse box, trunk fuse box and disconnected the glow relay - still 3.25 amps. I'm thinking of tracing the power cable, then pulling each of the ECUs. Does anyone have guidance on how to proceed?

Thanks,
Sixto
93 300SD

[Moneypit SEL]

You're on the right track. Removing power while watching the amp draw is the only way to track something like this down. Don't forget to check items that don't have fused power, like the alternator.

[sixto]

I disconnected the big and small wires at the alternator and starter, and the small wires near the battery. The only thing I can't trace is the big cable from the battery to wherever it goes. Still 3.25 amp draw.

alldatadiy doesn't have a diagram that shows distribution or routing of the big cable.

Other thoughts?

Thanks,
Sixto
93 300SD

[david s poole]

this is 140 body.plenty of things get power when key off door assist closing pump,central door lock pump[the probable culprit],dome lights,floor lights.can't think of others but could be.

[david s poole]

oh yes automatic antenna motor.

[Mike Freeman]

Some good advice before testing battery drain; Make sure of the following, remove key from ignition,all interior lights are off including rear dome and vanity lights,trunk light bulb removed and radio off. After connecting amp meter allow more than 120 seconds before reading the draw (Closing assyst and centrl locking usually run 2 mins. if leak is present)
The normal draw on these cars is higher than you would expect!
good luck Mike

[sixto]

alldatadiy has a list of acceptable current drain depending on options. Even if everything were drawing the max at the same time it's not quite 1 amp.

I checked draw with all the fuses out of the engine bay and trunk fuse panels. As in all fuses out at the same time. Starter, alternator and glow relay completely disconneted. All engine bay ECUs outside the engine bay. I did everything I could think of to frustrate those electrons. Still 3.25 amp draw.

The alldatadiy diagrams are all downstream of the fuse panels. I'm looking for a diagram of the wire paths to the fuse boxes and unfused circuits. Sigh.

Thanks,
Sixto
93 300SD