Questions and Answers

Mercedes 300D Glow Plugs Q. Hi, I own a 1984 Mercedes Benz 300D turbo diesel. I think there may be a problem with the glow plug relay. I read voltage at the plugs and after a short time, can here the relay physically cut off the voltage. The indicator lamp isn't lighting, and I couldn't pick up a reading at the pin on the relay that goes to the lamp.

Any suggestions I could try before spending money on a new relay that seems to be working fine except for that?

Regards,
JWY

A. The Glow Plug indicator lamp failing to light indicates you have two or more bad glow plugs.

What you can do is pull off the power strip going to the glow plugs and test each glow plug. Take a test light and connect it to the Positive (+) battery terminal. Now touch the tip of each glow plug. If the light comes on, the glow plug is good. If the light does not come on, the glow plug is bad.

If you find one bad glow plug, you best bet is to replace all the glow plugs.