Glow plug light comes on but plugs don't work...

[j.bronkema]

If anybody has any pointers on this I'd greatly appreciate it...

The dashboard glow light comes on per normal but does not turn off -plugs are not heating.
I pulled what I believe is the relay off and cleaned the contacts, checked all fuses, etc. (on my '76 300d the relay sits under a fuse bracket on the driver's side, yes?)
The car started after this, though I'm not entirely sure I really did anything.
Ran fine for an afternoon and a 20 mile drive but once again, a glow light and no start the next day.
Also, I have a frayed short ground wire on what I assume is a thermostat (2" blk cap that screws into side of block, wire goes to 1st GP)

I realize that this is all probably very elementary, but once again, I've never worked on GP's previously.
Anyone have any starter advice as how to go through the system?

[kerry]

Check your plugs. Loop plugs are OE on your car. If one goes out, they all go out. Your system also needs a ground wire. If the wire you reference is the main ground and it is not functional it would account for the system not working.