HELP, I have a 300D 1983 Mercedes, all glo plugs good, new glow plug relay installed, all wires tested, ignition sw disables glo plug when turned all the way on, problem is that the glow plugs and lamp only stay on a few seconds, not long enough to get them hot. I searched the wire harness and found one wire from the glo plug relay going to the fuel guage of the dash, it does not say if it is supplying a voltage or not to it but the guage shows empty, I assume this is a safty device. the wire is a W/bl g connected to #15 on the glow plug relay. To temp. fix this do I apply 12 volts to it, ground it or should I just sever the connection till I can afford a new fuel sender unit?

A few seconds sounds pretty normal to me. Not only that, but the light has nothing to do with how long the glowplugs stay on, they keep going even after the light turns off. Hook up a voltmeter to the six pin connector on the relay, then turn the key, you'll see when it stops giving 12v to the glowplugs.

If you are in a very quiet area you can actually hear the glow plug relay click off after about 40 seconds or so. I usually let it glow till it clicks off and then start. I do not really use the light as an indicator of when my car is ready to start. On really cold mornings, I might glow twice before I start.

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John
1986 300sdl
1985 380se

I checked for the relay "click", it fired for 3 to 4 seconds then turned off, I verified the glo plug supply with a meter, the relay did shut down after 3 or 4 seconds. I called the distributer of the relay and of course their tec support isn't availble and "will call me back". They did, the current draw should be 12 to 16 amps from the relay to the main lead of the glow plugs then the current draw should drop down to 8 to 9 amps when temp is reached. If current is around 8 to 9 amps to start with then 1 or more of the glo plugs are bad, AT $150.00 a pop I'm screwed!

I will let someone else help you with your problem only because my car does not have a relay system. I can tell you that if you go to fastlane at the top of the page they have Bosch glow plugs for $15 dollars. So if someone wanted $150.00 I would check other places for your parts.

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1973 220D "Emerson"

You could look in the archives to determine if your car has a temperature sensor in the head that tells the relay the engine is still warm/hot. If it does then the sensor might be bad.

There are two different systems used but I do not know the one your year uses. The second type does not have a head sensor I believe.

Sounds like the timer in the relay is not working correctly. Barry is right that the later relay has a temp sensor built into the relay itself and does not depend on the sensor in the head. However, the temp sensor only controls the length of time the light stays on and not how long the relay operates. The relay should power the plugs for about 30-40 seconds independent of the glow plug light.

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1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13

I've seen Bosch glows NEW for cheap- 8.99 a peice. That was at NAPA

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Regards,
Ian White

1995 E300 Diesel w124 OM606
2014 E550 w212 M278 biturbo

2001 BMW 740i E38 M62 (past)
1981 300SD w126 OM617 (past)