PNP solved my immediate issue. Got several at my local yard, a mix of 300 and 240D units.

Now have 2 good working units. An original MB and a Hella unit. Trying to get more info on the Hella from them but no return call yet.

For anyone else with this issue a real easy way to see what is happening is with a pair of alligator clip jumper wires and a nice cheeepie meter.

Clip one jumper on the negative battery lead and the negative of your meter, one to any available glow plug and the meter positive lead with the meter on the 20 volt DC range.

I propped the meter up on the windshield so I could read it while starting. Key on and instant voltage, start and almost immediately the voltage drops to zero.

If the GP relay is bad then from what Ive learned two things will happen.
1st, no voltage at the glow plug.
2nd, always have voltage on the glow plug which overruns the ability of the alternator to keep the battery charged.

A $5 cheepie meter and a $2 PNP relay solved the immediate issue. Far better than buying a new one for around $200.

__________________
1985 300D 198K sold
1982 300D 202K
1989 300E 125K
1992 940T

"If you dont have time to do it safely, you dont have time to do it"

"The democracy will cease to exist when you take away from those who are willing to work and give to those who would not."

Stuck out with Hella. Its an OE part so Hella is not able to release any info on the part.

__________________
1985 300D 198K sold
1982 300D 202K
1989 300E 125K
1992 940T

"If you dont have time to do it safely, you dont have time to do it"

"The democracy will cease to exist when you take away from those who are willing to work and give to those who would not."