Glow plugs

Can anyone help me with the glow plugs on my 300D? The "wait to start" light will not come on. I guess they dont work because the car is hard to start when it is cold.
Is there a relay? Where is it located? Can it be repaired, or do I need a new one? Can I do an easy test on the system?

Thanks for the quick reply!! This site is awesome!
My car is a 1981 model 300D. It has 146,000 miles on it.

can you give me a little more detail on this test process?
Should I use a 12 volt test light?
Thanks again, Steve

[Ron Johnstone]

What year is your car? Assuming that it is one of the older versions, make up a short jumper out of #12 wire with alligator clips on the end and jump each of the terminals, in turn, of the glow plugs on the engine block until the light comes on. When the light comes on, the jumped glow plug is the bad one and must be replaced, although it can be argued that it is smart to do all of them at the same time.
Keep the jumper with you to get you going if one fails again.

Ron's advice is good if you have a serial glow plug model. We MUST know what model you have to give you accurate information.

Have a great day,

[mikemover]

After you start the car, does the glow plug light blink? If so, that is the car telling you that one or more glow plugs are bad. And the previous posts are correct, glow plugs are inexpensive, so if you're replacing one, I'd go ahead and do all of them to insure easy starting. If your car has paralell-wired plugs, Larry's right--the jumper test won't work on those. You could also have a blown fuse on your relay, so check that too. The relay should be bolted to the fender well, or the firewall, depending on the model...just follow the wires from the glow plugs. The first thing you come to will be the relay.

Mike