W124 300D - Constant electrical load

[fastpakr]

Haven't driven my 87 in a couple of months, needed to put a new set of tires on it and get an alignment. My father tried to start it a few days ago and the battery was completely drained. We pulled the battery and recharged it, and the car will start now. However, when connecting it, there's a large spark present when connecting the ground side, as if there's an existing load on the system (and by appearances, something more than just an interior light, etc.). We pulled each fuse in the underhood fuse box one at a time, and tapped the cable on the ground post. The arc never went away (it's large enough that it generates a bit of smoke and marks the post - play with it long enough and you could probably weld the cable to the post. The battery light on the dash is on constantly (even without the key in the ignition).

Any ideas on how to trace the source of the load/battery drain/dash light?

[rallen]

Are there auxilliary fuse boxes you have forgotten to check? How about the starter motor? Is it possible to disconnect it? Else sounds like a leak/short somewhere.

[fastpakr]

It's possible that there are auxiliary fuse boxes 'somewhere', but I'm really not sure where. Could somebody familiar with the early 124's give me any info on all fuse locations? Regarding the starter motor, the starter still functions fine - not staying on or anything like that, so it seems an unlikely source.

Thanks for the ideas...

[mpolli]

There have been lots of posts on the subject of draining battery, like maybe a million, OK slight exaggeration, but if you search on "draining battery" I think you will find lots of posts, some of them quite lengthy with lots of ideas on what to check. This is definitely a recurring theme. Off the top of my head I remember a few of the many possible causes: Trunk light on all the time, bad voltage regulator, bad alternator diodes, aftermarket alarm, radio malfunction. There were others also. Give search a try.

Mike

[fastpakr]

A number of those were covered by checking the primary fusebox, though. I will be doing some more searching today or tomorrow when I have time... I think what concerns me most is that the amount of current draw appears to be rather extreme (let's just say I wouldn't want to have my hand past the insulation on the ground cable when connecting it).

[theairboy]

Try disconecting (all) the wires from the alt. lg and small.

Be careful making arcs to the battery post, especially in a confined space. Loud noise followed by serious injury may result . Seriously, I wouldn't do that.

I sounds like you have a significant ground. All I can suggest is disconnecting things one at a time and using a multi-meter to check for shorts. Good luck.

[fastpakr]

This car was put on hold for some time in the middle of wedding plans and moving into a new house, but it's back on the front burner now. I confirmed that unplugging the alternator eliminated the short, and dropped it for a bench test at Advance. It tripped the circuit breaker on their test machine three times, so I dropped it off last week at an alternator/generator repair shop. Hopefully I'll know exactly what went wrong sometime today.