I have '85 300D 617 and the on dash glow plug light works intermittently as does the relay. I can hear the relay popping appropriately when it's working but more and more often the relay isn't working and and the dash light doesn't come on either. I tested the relay according to the great tutorial on Dieselgiant.com and everything checks out. I tested the wires for excessive resistance and the pulled the glow plugs to see if they lit up. Everything works. Except... except when it's cold (30*F or less). More than likely when it's cold the glow plug system won't perform. Honestly, the system works famously whenever it's warm but not when it's cold. I'm at a loss. Question: do relays go out by performing sporadically for a while before they finally die completely? I was under the impression they would just quit, not die a long, lingering and frustrating death. I don't mind buying a new relay if I knew that would fix it. Thanks everybody, I appreciate any help or ideas you can offer.

Check the strip fuse in the relay. It may be broke or loose or have corrisition.
JOHN

Where did you get that impression? The timer is controlled by a solid state device, so it is absolutely capable of displaying a myriad of unusual behaviors. Absent a fuse problem or a bad connection on the smaller connector, it's probably time for a new timer.

Thanks for the responses. The strip fuse does check out. I wasn't aware of a timer for the relay. Is that located within the relay box or is it somewhere else?

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1985 300D 260K
1974 280 180K

All in the black box.

what you describe is exactly what happened in my 1985 300d turbo. I checked everything twice, and still had intermittent problems. REplaced relay with a new unit, and have not had a single problem since. Double check all connections, and if thats not it, it's probably a dying relay.

I'm on it tomorrow. I just wanted someone to confirm my suspicions about the relay. $98 for a new one doesn't kill me but I hate throwing money against good working parts. Thanks again.

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1985 300D 260K
1974 280 180K

me too I figured after 360K It probably deserved a $100 relay AND new glow plugs.

I know....I know... the glow plugs are probably spoiling the old girl...

You did the right thing. There is a lot of threads were members have not done the trouble shooting that could have been done with a $5 or less multimeter and replaced the GP relay only to find out it was the glow plugs. Intermittent problems are the worst PITAs.

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84 300D, 82 Volvo 244Gl Diesel