1983 300D Turbo
I just purchased this car last week and it has been running fine, yesterday a problem developed, the glow plug lamp stays on all the time. Wife took it to the store- maybe 15 minute ride and the car wouldnt start. I jump it and it did start but when I got it home it wouldnt start again. I think the plugs may actually be staying on and drawing so much power that the battery (new) runs down.
Any pointers as to problem appreciated.

Great site!

There is a time relay that controls the glow plugs. They should stay on for about 35 sec then turn off (light turns off sooner depending on temperature of engine). Put a volt meter on one of the connections to a glow plug and see if they are turning off. If you don't have a voltmeter, you can use a small 12 volt light bulb in a socket with wires. If they stay on, you probably need a new glow plug relay. The glow plugs will drain a battery quickly because they draw more than 50 Amps.
P E H

I opened up the control box on the firewall, there was moisture inside which I dried out, there are two sets of contact points which were corroded so I cleaned them up with emery cloth. Now everything is okay now.