I have an 87 300SDL turbo and I have a very strange electrical problem. When I take the key out of the ignition the all of the warning indicator lights turb on. When the key is in the ignition (and while the car is running) the lights function properly. The only light that does not function properly is the glow plug indicator, however the car starts, and runs, just fine.

I need to disconnect the battery if the car is parked for more than a few hours or the lights drain the battery. When the battery terminal is connected to the battery, there is a lot of sparking and there are quite a few relays clicking on and off. The water pump remain on as well when the battery is connected.

I have replaced the alternator and the ignition switch already and the problem has not been rectified. Also, by pulling fuse number 15 (interior lights, central locking, etc etc) the panel lights turn off and everything seems fine.

I have noticed the glow plug relay does a lot of clicking, and was thinking that could be reponsible for this.

I am at my wits end with this problem, please let me know if anybody has any ideas. I would greatly appreciate any ideas.

Thanks.

Any aftermarket electronics installed? Alarm, remote starter, stereo equipment, etc?

There is an alarm installed, but it has been present since the car was purchased. The car was purchased new in early '87 and the alarm was installed by a shop in CA that specialized in exotic cars that very same week. The car now has 142K, and ~15 years of use. I have pulled the fuses on the alarm, but the problem continues.

This is a very, very frustrating problem. I appreciate your time for posting, and please keep the ideas coming.

Thanks.