Where is the glow plug relay on the 1978 300D. Not on the fender or behind headlight. Thought it was one of the two silver boxes underdash but when I uplugged each one the glow plug system still functioned. Anybody have a pic?
I never here the relay click off when the light goes out. Doesn't happen a minute later either. I haven't solved my charging problem and I wonder if the relay has failed and is drawing current and preventing proper charging.

thanks

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Kevin

1978 300D
1979 240D

Trace the wires backwards from where they are attached to the Glow Plug.

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84 300D, 82 Volvo 244Gl Diesel

It is a silver box bolted to a pedal arm support area directly above your knees when in the drivers seat. You remove the underdash cardboard on the drivers side to get to it. This is of course if it is identical to my 77 300d and I think it is.
The underhood relay emerged with the non series glow plug introduction I imagine. You may have already looked at the relay I suspect. It has been quite a few years since I last dealt with mine so my memory does not allow for a good relay itself description. Other than a silver box about three to four inches wide say five inches tall and maybe inch and a half thick.

I think we are talking about the same relay, but curiously, when I pulled the connectors, the glow plug light on the dash functioned normally when I turned the key. Is this just a timer circuit with no connection to the relay function?
I'm looking into this because I thought it might be drag on my charging system and that would explain why my alternator is not charging the battery.

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Kevin

1978 300D
1979 240D

Simpler to pull the strip fuse in the engine compartment for the glow plugs and check for charge.