I have one trick to add to this thread. I also noticed my dash light for the glow plugs not coming on and engine wouldn't start.
Testing at the 5 pring plug I found not current going to the plugs, to I popped the cap on the glow plug controller board( is this what you are calling the relay?)
Anyway, I foudn that the engine started quicky if I held down the contactor amnually for about 20 seconds, it'll emit a tiny blue spark when contact is made.
I also figured the board needed replacemtn because of a few spots where it had browned(like overheated)
Good emergency start. Looking forward to getting the updated board.

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1972 220d Blew motor twice! ouch
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