Disconnected glow plug relay. But light on dash still comes on?? - PeachParts Mercedes-Benz Forum

cook · #1 02-04-2007, 09:08 PM

84 300D

I unplugged both plugs on my glow plug relay – the one that goes to the glow plugs, and the one that comes from the ignition switch, goes to the ground and pre-glow light on the dash. The only thing connected to the relay is the big power cable.

Based on the factory CD wiring diagram, I expected that unplugging the two plugs on the relay would make it impossible for the pre-glow indicator on the dash to come on. The diagram shows only one connection to the pre-glow indicator, and that is from the blue/white wire that is on the plug that is not connected

But guess what? It comes on when I have the key in the “On” position.

I did a search in the forum, but did not see this situation described.

Does anyone know if the wiring diagram is incorrect?

If it is, how can I get an accurate wiring diagram for this pare of the circuit?

cook · #2 02-07-2007, 09:25 PM

Still trying to figure this out.

Could I ask an 84 300D owner to try something for me to see how their car acts?

Please disconnect the two connectors on the pre-glow relay. They turn the key to the “on” position and let me know if the pre-glow light on the dash comes on or not.

If I read the schematics right, they say that the only way the pre-glow light on the dash can come on is when it gets power from the pre-glow relay. But mine will come on even if the pre-glow relay is not connected.

Very confusing!

Thanks

holthoff · #3 02-07-2007, 10:43 PM

The only thing I can think is that maybe behind the cluster the glow plug light has been accidentally swapped with the seat belt light.

Mine was like that once. For a few weeks, I kept thinking it was kind of funny that the glow plug light kept going out right around the same time as I buckled my seat belt. Hmmm...

Of course if your seat belt light still works, then it's something else.

toomany MBZ · #4 02-08-2007, 06:03 PM

On the CD. Removing the four pin plug resulted in no GP light.

cook · #5 02-10-2007, 08:10 AM

ToomanyMBZ: Thanks for verifying how it should work.

Holthoff: Yes, that must be it. I noticed yesterday that the seat belt buzzer goes off the moment the glow plug light goes off!! I will get behind the instrument cluster today to verify, but that has to be it. Thank you!!!