Hi
I just bought a 1982 300SD. The glow plugs are not working. Found the procedure for checking everything out. This is my first diesel, so bear with me.

I have main power. The fuse has power both ends. With the relay apart, there is power at the solenoid.

The relay looks almost new on the inside. The one contact has minor arc mark. The secondary contact is new.

With the 4 pin plug off, I have voltage at pin 1, the red wire, with the key on. I do not get a glow plug light on the dash. If I jump 1 and 3, I get the dash bulb, so it works.

I took the 4 pin plug apart, to tighten / crimp the connectors a bit. with the key on, I plug/unplug the 4 pin pin plug, the relay pulls in, but imediately releases, so I figured I had a bad connection.

The connectors are very clean.

I plugged them in without the plug body on to check voltages and grounds. Everything checks out. I then checked for volatge and grounds on the inside of the relay. Everything is there. But again, if I pull off / put on the red wire, the relay pulls in but immediately releases.

I get this reaction whether the 5 pin glow-plug plug is attached or not.

I've only had the car for a few weeks, but this relay looks brand spankin new on the inside. I read somewhere about charging an internal capacitor by energizing the coil a number of times, I've done this, but still the same results - the relay drops out as soon as it pulls in.

Any simple fixes - or do I buy a brand new relay? I gotta tell you, this one looks brand new on the inside. Outside ain't too bad looking either.

Hoping it is something simple
Fred

*****More questions - I bench tested it. Ran negative 12vdc to pin 31. Positive on big lug 30. Jumpered from 30 to 15. The solenoid pulls in, but immediately drops out. Pin "LA" feeds the dash lamp. Anybody know what pin 50 is for? The sheet I have says it goes to the back-up lamp? Huh?


BTW - with no glow plugs, she started in 6 degree weather here in Wisconsin week ago!
It was a Florida car before a few weeks ago.