Hello,
My glow plugs don't come on like I believe they are supposed to in my 83' 300SD. Sometimes but, rarely do they come on when I turn the ignition on. I can turn it off and back on and the still won't after repeated attempts however when I try to start the car - it turns over usually doesn't start but, the next time I turn the ignition the glow plugs come on and the engine starts fine. Any idea what is causing this?
Thanks,
Tom Martin

TNM,

Try pulling off the cable connectors on the GP relay and reconnecting them. Do this about 5 to 10 times. If there is corrosion on the connectors, this should clean it off. There are 2 connectors.

Worked for me.

P E H

How can I find the Gloow plug relay - is it in the engine compartment or where?
Thanks,
Tom Martin

On the SD, It is down on the left front wheel well inside the engine compartment. It is rectangular (kind of) and it has a black cover that slides off. As haiges said, pull the bottom connector cable on and off a few times. Also, ck the blade fuse to make sure that it is tight. This is "HOT" all of the time so dis-connect the battery or be careful tightning the screws on the fuse. Also ck the 10mm nut which is the main input power cable. I will try to attach a few pictures off of my wifes '84 wagon. (same box in the same location). Can't attach them right now... I have to figure out how to reduce size. I'll re-try in a few minutes.

Lets see....

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My Truck.. 2007 DODGE, 5.9 Cummins, 6spd stick, 4X4. My car..1977 240D, OTHER WHEELS...1955 VW Oval window bug, European Delivery (Holland) with a 1700cc, 2 barrel, Porsche drum brakes. 1939 WILLYS Pick-up. 1967 Triumph 200cc Tiger Cub. 1976 Honda 550F 4cyl Motor Cycle.