Originally Posted by MS Fowler

I think he did get the relay, except that he ordered the wrong one and it was for the 4 cyl; not the 5, so he can't use it.

I am "assuming" that if we can locate a hot wire that the relay will take care of all switching/timing issues.

Failing this, has anyone installed a manual " push top start" momentary contact switch to run the glow plugs? I would use a relay to ahndle the heavy current; the switch would only carry a very light current.
( I have done this on my F250 Diesel--their GP controller was a menace. Ford installed 6 volt plugs in a 12V system to get faster starting. The controller was supposed to cycle the plugs to keep them from frying on 12V. They would only tolerate about 15 seconds before burning out. I saw my controller comeone while driving down the road at 50mph with a warm engine. They were burnt out before I could even stop. I switch to 12V GP and a manual push button, and haven't had any problems in 6 years or so. But this is a Ford--do Mercedes folk tolerate such re-engineering of these machines?