Waiting 45-50 seconds every morning for the old loop plugs was a bit excessive. On the W115 300D's the original relay will NOT work with the parallel pencil plugs(Bosch Duraterm #80035), and i did NOT want to have a rigged push button under the dash and a ford starter relay to operate them...i wanted to retain the original function of the system.
So I decided i would get a complete wire harness and relay from a turbodiesel W123 or W126 and install it in my W115 so that I could use the pencil glowplugs.
Here is how it is wired:
The turbodiesel relay:
PIN LA- glowplug light
PIN 31- ground wire
PIN 50- violet wire(starter signal wire, same color at old harness)
PIN 15- relay wire(black/blue/green wire, at original harness)
12V constant from the battery
So i ran a harness from the turbodiesel relay under the hood to the old harness at the original relay under the dash and spliced into 2 those wires(blue/green/black, violet).
Then I ran the GP light wire up the light socket, and grounded the other side of the light bulb.
Then i put in the glow plug wire harness that goes from the relay to each GP, which i pulled from a 1984 300SD at the junkyard.
Im very happy with how this updated system works, it is wired up exactly as it should be and nothing was rigged. None of the original wiring was damaged and I could return the system back to the stock loop plugs and relay system very easily.
The car starts up great when the GP light goes off(about 4 seconds). Never has the car started so quickly. I plan to make a movie tomorrow morning to compare to my old cold start video when it had loop plugs.
Here are some pictures:
