1981 Mercedes Benz 300d • 5 cylinder 2WD Automatic • 220 miles

Hello! My vehicle is a 1981 mercedes 300D. I have just replaced my glow plugs. I worry about the relay failing, my glow plugs staying on and having a shorter lifespan. I am considering opening the hood each start, and inserting the fuse [the breaker located directly over the LF wheel], starting the car normally, removing the fuse, closing the hood, and storing the fuse in my glove box until the next start. This sounds like a nuisance to me. Is there a less cumbersome way I can be assured my glow plugs will be on ONLY when I want them on, and thereby have longer lifespan?
March 9, 2011.

Suspect control unit temp resistor faulty see diagram. If operating will not allow plugs to have power over 25 sec.

Mar 9, 2011.
Most impressive answer by Docfixit, Here's another question, please.

I have a 1975 Mercedes 300D which has ignition and/or glowplug and/or relay issues. I assume (always dangerous) that this relay is a box of primitive electronics?

The only parts which I can see listed are M-B units at $350 or thereabouts. Is there a reputable supplier at more realistic pricing?

I guess that I should also ask whether one can test this relay? Other than by "it don't work so buy another"

Any other ideas would be supa-welcome.


Nov 3, 2012.