1981 300D Non-turbo, I have been having problems with the glow plugs. When I turn the key to engage the glow plugs, the indicator light will not always turn on. Sometimes, if I "flick" the key from the glow plug position to off, repeatedly, the glow plug light will engage. To see if it was just the indicator light malfunctioning, I turned the engine over, when the light didn't engage. The car started, but very roughly. It was obvious that the plugs didn't warm up the chamber. Usually the engine turns right over, when the plug light engages. To add to the mystery, the battery light comes on, BUT only when the key is turned to the "off" position! To see if this was just some gremlins I left the battery light on and let the car sit for a while. Lo and behold, the battery had been depleted, but not enough to turn it over. Thinking this may be the ignition switch, I replaced it. Still all the same symptoms. Next, I pulled a couple of glow plugs, and turned the key to engage the plugs, no glow, without the glow plug light engaging. So I ordered a preglow relay switch(my next logical solution). I just got done installing the switch, and guess what? The same symptoms still persist. Only now the indicator light doesn't come on at all, even after "flicking" the keys around. The battery light still comes on too. Has anybody every experienced anthing remotely similar to this? I am at a dead end on this one. Could it be a short somewhere? What does the battery light have to do with the glow plugs? Also I should add, the glow plugs are really new(less than 5000 mi), and are hardly even carboned up.

you had the instrument cluster out lately? could you have the lights plugged in the wrong light space?

tom w

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[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.

Tom, when the seat belt light comes on, I fasten the seat belt, and the light goes off. I had the cluster out when I r/r the ignition switch. I was very careful to put all the connections back in the same place. I would also like to thank who ever it was that suggested grinding the steering lock bolt off. Thats a great idea. I also went ahead and replaced the lock cylinder while I was in the area monkeying around. I'm pretty sure that there's a short somewhere in the system. I'm in need of some suggestions as to where to start. I've always done a majority of my own wrench turning with cars in the past. This is just my first time screwing around with any electrical work(if that's what it is). This is also my first Mercedes. Problems aside, I am very impressed with the car.

check your fuse relay strip. mine cracked and all kinds o things happen. my glow plugs would sometimes come on, car hard to start etc. but when i replaced my strip $1.40 all was well. check your fuse too

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ez rider

I agree with the fuse inside the glow plug relay box.

If you have voltage at the relay box and no voltage to the plugs (any of the plugs), either the relay is bad or the fuse is bad.

Did the new relay come with a new fuse?

Hi,

I didn't want to start another thread so I hope you all don't mind reviving this one.

My GP light won't come on, but if I wait 5-7 seconds after putting the key to preglow, I start it and it starts fine. Sometimes it's a bit rough, but this morning it was the best start after months of having no GP light, 5 seconds only and it fired smoothly AND strongly. But the GP light never bothered to come on months ago. Took out the instrument cluster, replaced bulb while replacing dimmer switch and checking other connections, but the GP light still doesn't turn on.

I don't step on the pedal before or during the preglow or starting process.

GP relay (strip fuse) is intact. Didn't yet check each GP, I'm not electrically minded. How do I go about checking the GPs? I can buy a cheap voltmeter or multimeter but from there I don't know how to proceed.

Thanks.

That's what you need to do.

A cheap voltmeter, that also measures ohms, will tell you if one of the plugs is completely burned out (open). A better meter, which you probably should get, will give you the proper value of the circuit, in ohms.

Each glow plug should test at between .8 and 1.2 ohms.

You test them as follows:

Pull the plug on the side of the glow plug relay. There will be five sockets in the plug. Connect the meter to one of the sockets and ground.

Read the result. Repeat for all five sockets.

Any readings that are above 1.2 ohms (or infinite) tell you that you need a new plug.

Note that you have failed to provide the vehicle year and model, so, I'm assuming that you have a 617 with the later model parallel glow plugs. Otherwise, everything mentioned above won't apply.

Hi Brian,

Apologies, I thought I wrote my car model and year down. Yes, it's the OM617 engine, '83 Turbodiesel.

Thank you for the step by step help, but I have one more question. When you say you ground the other probe, do you just touch the car?

Like I said, I'm not electrically minded. Thanks again!! Yes I might also get a better one, I figured I might need it in the future.

It would be preferable to connect the probe to the negative battery terminal. Any slight resistance between the body of the car and the battery terminal will affect your readings, so, the terminal is best.

You may wish to put the vehicle in your signature. The software will put it at the bottom of every post that you write. I don't ever manually write the two vehicles that you see below.

Thanks again, I'll remember that when I get home. Just updated my profile and signature, hope you like it!

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http://farm8.staticflickr.com/7271/7...144c3fc1dc.jpg

Anytime.

I do like it, however, the photos will show up after every post that you make. This lengthens the thread, uses up bandwith of Mercedes-Shop, and causes the dial-up users to scream bloody murder. Although attractive, we have all seen the star before.