1995 300D, 165K. Runs great. Starts fine. Yesterday, glow plug lamp illuminated after car running for 20 minutes, then went out after restart. Turning on cold, no lamp. Turning off, then on again, glow lamp lights. Typcially, this would indicate one glow plug failed. (Off/on sequence twice with no lamp = more than one failed plug.) But...all plugs replaced in July, engine wiring harness replaced in August.

Where exactly is the relay and which terminal do I test. I actually think I've found the relay (in black box, 3"x3"x1", on driver's side front wheel well) and it does click when you turn the key. Seems OK. So now it's down to testing the plugs via the harness leads. Is there a a picture or guide anyplace?

Thanks-
Dave