83 240D glow plug relay question - PeachParts Mercedes-Benz Forum

funola · #1 07-22-2007, 09:28 AM

The glow indicator on the cluster only comes on for a 1/4 sec or so from a cold start and i do not hear the relay clicking off if I leave the key in the "on" position. I thought that was not right so I hooked a test light across a glow plug and sure enough, they are getting power while key is in the "on" position until the engine starts. If I leave the key in the on position to listen to the radio for example, the glow plugs will evevtually burn out being powered constantly.

This is not how a glow plug relay is suppose to work I suppose? I will try to repair it but if I do not have any luck, does anyone have a good used one for a 240D?

#2 07-22-2007, 09:37 AM

The relay should stay energized for about 40 seconds if you just turn on the key and wait, it should turn off when you start the car (if you don't have a post-glow relay installed). The indicator light duration should be dependent on temperature, but it should always stay on for at least a few seconds.

I agree that leaving the key in the run position will age the GPs (and run down the battery), that's what the auxiliary key position is for.

funola · #3 07-22-2007, 10:33 AM

So there should be a 40 second timer for the glow plugs? I don't think mine is working. I'll have to verify that with a stop watch next time since I think the glow plugs are staying on indefinitely in key position "2".

I didn't know there is an "aux" key position. One mine, position "1" just unlocks the steering, no accessories. "2" enables cig lighter, radio, Pwr windows etc. and is what I think is the "aux" position.

btw, where is the accessory relay located? I hope there is one.

#4 07-22-2007, 10:40 AM

40 seconds is just an estimate, but I think it's pretty close. If yours does not shut off, you probably have a problem with the GP relay (which might also explain your indicator light problem). The radio feed should be on position #1, I don't think there is a relay, just the ignition switch, for the "auxiliary" power.

funola · #5 07-22-2007, 10:45 AM

I have fixed the jumpy fuel sender on the 300 D by just shaking it and squirting in solvent. On the 240D, I did the same and fixed the jumpy fuel gauge but the reserve light is always dimly lit. Through resistance measurement of the reserve switch (290 ohms when it should be infinite), I think there is gunk at the bottom of the sender that is causing the resistance reading.

There is a round plastic stub at the bottom of the sender. Is that some kind of rivet? Can it be taken apart and put back together without breaking it?

Stevo · #6 07-22-2007, 11:08 AM

Quote:

Originally Posted by funola

There is a round plastic stub at the bottom of the sender. Is that some kind of rivet? Can it be taken apart and put back together without breaking it?

There is a sort of plastic thing that surrounds that tiny nut. I just preyed it away and disassembled the unit and put it back together with thread lock. Be careful the wires inside are very small and fraggle.

funola · #7 07-22-2007, 07:04 PM

Interesting that the "1" position in both my 300D and 240D does not work as "aux". Is that a common failure mode? Is the ign switch adjustable? Interesting also that there is no accessory relay. That must be a mother of a switch to handle cig lighter, radio and other accesories.

Kuhlrover · #8 07-23-2007, 12:37 AM

The glow plug light on the dash works some what independant to what is actually happening at the plugs. For example just because the glow plug light is on or off, does not relate to the glow plugs being on or off. (Strange isn't it?)

As the other guys have said, the glow plugs will stay engergized for about 40 seconds or so. You will also notice that on warmer days the glow plug light will stay on for shorter period of time then it will on colder days.

TimK

#9 07-23-2007, 01:17 AM

Quote:

Originally Posted by funola

Interesting that the "1" position in both my 300D and 240D does not work as "aux". Is that a common failure mode? Is the ign switch adjustable? Interesting also that there is no accessory relay. That must be a mother of a switch to handle cig lighter, radio and other accesories.

On both my W123s, the radio works in the #1 position, do you have after-market radios in both your cars? Maybe they were just wired to a different power supply than the original radio. I don't know of an auxiliary relay, but I don't have a wiring diagram with me. AFAIK, the only thing that words on the #1 position is the radio (not much of a load). I have no idea when the lighter works, I've never tried to use it.