On my 85 300D I started to have some crazy problems which I have tracked down to the glow plug system. I noticed while driving that the battery voltage would drop to 11 volts at night (12.5 volts when the headlights were not on) for a couple of seconds to what seemed like a minute and then the volt meter would pop back up to it's normal voltage of about 14 volts. I have traced this down to number 1 and 2 glow plugs coming on at arbitrary times. When it seems to do this is erratic so it took awhile to find this problem. I expect the alternator at first until I installed an amp meter inline with the alternator and noticed that when the voltage dropped to 11 volts the current from the alternator went up to 60 amps output.

I placed a volt meter on each glow plug and sure enough it was only 1 and 2 that were getting voltage with the car running and they would periodically go on and off. Everything else seemed to act normal. The light on the dash did not come on when this happened. If I turned the key to the start posistion but just jogged the starter and let the key go back to the on position the glow plugs would turn off which seemed normal but the other two periodically coming on was Freaky. So I ordered a new relay.

I got a new relay in the mail that I paid $119 for, it's made by Bosch out of Malaysia and It's worse then the old one. This relay won't turn off at all. Even after 45 seconds in the on position it will stay on. After the car has started it will stay on for what I timed up to a 1.5 minutes before I turned it off. This really made me scratch my head, question my sanity and choice of religion. I am looking for some confirmation from the folks on this website, but I think I was sold a bad relay. For now I have put the old unit back on. By the way I have check the plugs. I am getting about 0.7 to 1 ohms at each plug. Has any one else had a relay fail in each of these ways?

TimK