1981 300SD glow plug relay, HELP!
 

I have a 1981 300SD with a glow plug relay problem.
When the key is turned on the relay clicks twice, on then right off. The relay sends power to the glow plugs for just a second or two. I took the relay apart and cleaned the contact points and every thing looked ok. Is there anything else that could cause the relay to cycle so fast, the glow plugs don't get any power so it is very hard to start these days. The glow plugs have been replaced in the last 3-4 years, so I would hope they haven't gone bad yet. The relay seems to be my problem. Just want to make sure I not missing some other test before I purchase a new relay. I looked on FastLane and they have a relay with 4 glow plugs for $87 and just a relay for $120. Anyone know why the one with 4 plugs is so much cheaper.
Thanks for any advice you can give.

Martin
Edmonds, WA
1981 300SD 197,000 miles

I think it's called a "pre-glow time delay relay" or something. I almost bought one for my 1983 SD which I am 98% sure is the same as your 1981 SD.

I think the dealer wanted something like $155 for the part back in 1999, so the $120 sounds like the right ballpark. The cheaper one probably is for a 240D possibly.

I had my indy put in a used one last year; he only charged me $30, and I've been glowing happily ever since. Hope this helps, Bob

glow plug relay
 

Does your preglow light work correctly, does it flash, or not light at all, did you happen to do any voltage or resistance checks, also did you check the fuse, If you are not the type to mess with such things there is a relay on E-bay, its only @ $2.25 with three days to go.

http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&item=1857391980

Looks like this is the glow plug relay you've been looking for; it's only at $2.25 right now but it is a $120 part new... if you didn't have an immediate need for one, I'd be tempted to get one as backup at that price. In case I was stranded with just a toolkit and a used glow plug relay, I could put it in myself if I had to. (Never did one, but given a lot of time, good lighting and adequate tools, how hard can it be to change one relay?)

Thanks for the Ebay info, didn't even think to look there.
My dash preglow light stopped working, I tested it by jumping the 4 pin plug on the relay and the light works. The fuse in the relay is fine. I hooked a test light to each of the glow plugs and every time the key was turned to preglow the test light would come on for a brief second. This is why I think it must be the relay. It clicks on then clicks right off.
Thanks Bob and RSH for your input.