Where is the Glow Plug Relay? '83-300SD
 

I replaced all glow plugs maybe 1.5 years ago and they've been great and hot. One day the pre-glow light on the dash did not go on, and there was clearly no pre-heat taking place. The car will choke to life with some cranking and starts quickly if I plug in the block heater overnight. I want to find the relay and check it out or boil it or something, but don't know where it is or what it looks like.

It could be something else too I suppose; any comments on this? Thanks!

1983 300SD
375,000 miles

The relay is on the driver side fender -- trace the wires from the glow plugs back to the black box about 4" square mounted toward the front. You can pull the cover off the relay and check the 80amp fuse 1st. But if you have 2 bad glow plugs you can get the same symptoms even with a good relay and relay fuse. Check the glow plugs, even though yours are relatively new. Quick and easy glow plug check: use 12v test light. Remove the relay cover. Attach aligator clip to the 80amp fuse link under the relay cover and then touch the probe to the nut on each glow plug end. The light in the test light should glow on each plug. It will not glow on any bad glow plug.

Check that fuse closely. Occasionally they crack slightly and do not conduct voltage.

exactly what happened to me the first year I had the car.