mmcg330

I purchase a 89 300SE in the summer of 2010 and all mechanics/electrical functioned without any issues. As soon as it turned cold it seemed all heck broke loose. The power door locks would not work, ie when I go to lock doors with key only door with key would lock. All others would stay open so now I have to lock each one individually.

Secondly, when I close door the dome lights stayed on. I made sure the switch was in correct position so lights go off when door is closed but that did not work. I now have dome switch in off position.

Lastly, the car dies while driving sometimes and I have to get a jump to make it home. The altenator light does not come on or has not come on. Based on a couple of posts I have read, it was suggested to change the voltage regulator, which I did. I recharged the battery and drove for a day without issue. I let it sit a couple of days and went to start and it would not start. I should also note that the battery that came with car is a standard battery you would get from Kmart/Sears. It is not the large Exide type battery recommended for car.

It seems something is draining the battery that I can't see or figure out or maybe the altenator is not working.

Anyone have any more suggestions I can try. Thank you

WGB

I had a 1987 300SE that did that from new and I finally diagnosed it myself with a small ammeter. I found an intermittent 2 amp drain when the car was supposed to be off which would come on for 2 minutes and then go off for two minutes. Very confusing but would stop when I pulled teh fuse to the Hirschmann antenna.

It turned out that the Hirschmann is supposed to sense when the motor has stalled at the end of it's travel and turn itself off electronically but mine wasn't so the motor would continue to drain current until it overheated then the overheat cutout would turn it off until it cooled down again.

If you drove the car every day there was no problem but two days of parking would drain the battery.

The first owner had sold the car after 18 months (with a new battery fitted) and the agent never figured it out.

I also replaced the battery and the voltage regulator first.

It cost $75 for a new electronic module inside the Hirschmann and I kept that car for 5 years with no further problems.

Disconnect the negative terminal of the battery with everything turned off and connect a $10 ( probably only need a 2 amp model) ammeter between terminal and cable. There may be some activity for a couple of minutes while phoines and things sort themselves out then you should see the clock ticking in the ammeter and nothing else. If it is drawing any current start pulling fuses until it stops.

Bill

mmcg330

Thanks for that info, I will certainly give it a try. Now this may be a silly question, but I have worked with ammeters a couple of times but never on a car.

When you said connect ammeter with terminal and cable after disconnecting the negative cable, do you mean that I should connect the (+) cable of ammeter to the (+) terminal on battery and then connect the (-) negative cable of ammeter to the ground cable? I have seen that suggestion but it was not clear to me. Thanks.