strange battery drain 94 e420 124

[wally]

I have had occasional drain of my battery over the last 7 years of owning this car. If the car sits for 2-4 days, the battery will be down to 9-10 volts and unable to turn the engine over (even with a new battery).

To monitor the situation I have a voltmeter installed in the car. If left overnight the battery voltage is usually around 11 - 11.5v when starting the next morning (key on after fuel pump shutoff).

The charging voltage is 14.2-14.3v, so it appears the alternator is working. I had the alternator tested several years ago and they said it was OK. One issue with the alternator is that sometimes when starting the car (usually when hot) the alternator isn't immediately working (reading is 11-12v) When the engine is revved up the alternator kicks in and voltage stays up when going back to idle.

Occasionally the radio will stop working (head unit works but no amplification) and more recently both the radio and door locks quit working.

Today I am trying again (I think for the 4th or 5th time) to figure out where the drain is coming from. I have reduced it to something on either fuse C or fuse 9 and I have eliminated some components.

I noticed a relay click when I removed fuse C. The draw at fuse C is 12ma. Probably this is the current needed to keep the relay closed? Not enough to drain the battery so I leave fuse out and move on.

With fuse C removed, I notice another relay click when fuse 9 is removed. The draw at fuse 9 is 300ma!? Also the dome lamp will turn on (with doors closed) but will not turn off.

I would think that there should be no relays clicking when any fuse is removed?

The relays A and F are the ones involved. If I remove both of them, the draw goes away at fuse C. If I leave one of them in, the draw persists. I can now replace fuse C and fuse 9 and most everything works except for power seats, windows, and sunroof.

Now here is the weird part. If I put it all back together (relays, fuses) and check draw at the battery I read 25ma, an acceptable draw! The radio and door locks work too. So somehow the fiddling I did (removal and reinstall of a few fuses and relays) caused a change.

Since the dome light comes on, it seems like something "thinks" the doors are open? (with fuse C removed, otherwise it works). So I disconnected the front door switches, that did not help.

I also disconnected the warning control unit and anti-theft unit and no change.

So based on all this, I think I have a short that comes and goes in the door wiring. Since the door wiring consists of power seat and power window stuff (which is what relay A and F are supposed to be for), it fits.

Am I on the right track here? Any comments much appreciated.