Maybe its built into the relay then...I remember on my 82....when the engine was cold the gp light would stay on for a bit when the engine was cold....once hot it would stay on for about a second....then go off....so something has to be telling the rely the temp of the engine....

The 83 240D stock glow plug relay does not have an external ambient sensor. It is internal to the relay.

When my 240 had a dead glow plug it was very difficult to start. 1 pot down out of 4 is not a good thing.

Fortunately on the 616 it is very easy to change the glow plugs. I did mine in about a half hour with just an open end wrench.

A 12 and 8mm gear wrench will help.

Unfortunately, the circuitry needed to support that theory does not exist. The temperature being measured is that of the engine compartment, not the engine itself.

I have to agree that GP is the most likely culprit but as charmalu said, try pumping the primer a couple times and see if there is any improvement - you may have a slow leak that causes temp fuel starvation. Maybe both.

A 240D should kick right over if all is set well. Just a 1 or 2 sec bump and she's running.