I went out to start my 84 300SD this morning, and the glow plug light would not illuminate. Having been through that before, I suspected that I had one bad glow plug, but the other 4 would be sufficient. I tried starting the car and it would not catch. It was about 40F in the garage, so it wasn't _that_ cold. No go.

I measured the battery output with no load: ~12.5 volts. I monitored the voltage while the glow plugs were _supposed_ to be glowing and saw no voltage drop so I suspect that they are not being energized.

I measured the resistance of all 5 plugs - all were within spec. I examined the 80A fuse and it was fine. The plugs are Bosch, and are about 9 months old.

While cranking (at a healthy speed, I might add) I did notice smoke from the exhaust that smelled very rich, so I believe I have fuel.

So, I am thinking my glow plug relay is toast. I am ready to run to the dealer and grab one right now ($130) and give it a go.

Anybody have any better ideas?

Chris Blanchard
1984 300SD 165k
Cincinnati, OH