Hi everyone-

I recently aquired a 1976 115 chassis 300D Mercedes. It was running, but then I had to have the starter rebuilt, and I changed all of the glowplugs (older filament loop type). After the starter and plugs werereinstalled, the glow plug light would not come on and, in fact, there is no power to the glowplugs at all. There is no strip fuse on this model, and I can hear the underdash rely click on and off when I turn the key. I have also replaced all the old ground straps, etc.

I do not want to spend $125.00 on a new relay as a troubleshooting measure, if that isn't the problem. I have also noticed that the 8 amp fuse #4 (which controls the turn signals, etc. blows everytime the key is turned to position 2, could this be related or just coincedence?

My problem points to a faulty relay (which was installed in 1991) but I wanted to be sure before I invested the extra money. Thanks!

I'm in a similar position. I bought a 1976 300D. I changed the glow plugs - and the fuel filters - and it wouldn't start any more.

Is the relay in our model different than the relays in the 300D W123 model? I notice that other parts of the system are quite different. If it is the same relay as in other 5 cylinder diesel models, and you are changing it just to see if changing the relay will fix the problem, it might be easy to find.

The relay in our chassis model is under the left hand dash panel rather than on the inside fender of the w123's. I have decided to replace my entire glowplug system with the newer pencil type glow plugs, and have purchased a kit that allows you to completely bypass the old relay and control the glow plugs with a manual switch. I'll keep you updated as to whether or not this fixes the problem. You can check the kits out at **************.com under the diesel specific parts.

Do you have the gorilla knob? I have a 1976 240D (W115), and I have a knob I pull to energize the GPs. Turning the key to 2 doesn't do anything except unlock the steering wheel and allow the car to start.

I also don't have a relay for the GPs. They are wired in series, so if one goes bad (or is not wired correctly) none will work. Maybe there is a bad ground at the end.

If you do have a GP relay, and can get to it, try jumpering across the proper contact to see if they glow.

I attached a scematic to this thread, it might help:
http://www.peachparts.com/shopforum/showthread.php?t=165381

-G

my car doesn't have the gorilla knob. It used a timer relay located under the dash. I have now installed the faster pencil type glow plugs and a manual override switch for the relay. Unfortunatly, now every time I turn the ignition, the #4 fuse in the main fusebox blows and cuts off the 12volt power source that is feeding the glowplugs. Any ideas on how to fix this problem? I've ordered a wiring diagram from Mercedes Classic Lit, but they are taking their time getting it to me!

I converted my 73 240D to the pencil style GP's. I ran a separate line from the battery. I used 10 gauge wire through a voltage relay activated by the new timer box. I had to install the new timer relay control because I had the old Gorilla knob.

I'm probably wrong on this but I believe you have to change the timer control from the loop type to the pencil style also.

There should be no direct power supplied to the GP's from the fuses.

well, I completely bypassed the old timer relay. Instead, I installed a manual relay that works with a button that I push when I want the glowplugs to light. How did you go directly from the battery though? I might be able to reconfigure that way to get her to start.

12V lead from the battery positive terminal to the relay. I THINK #85. #87 to the actual positive terminal output on the timer/relay. Ground was #30. I believe #86 was "switched" by the ignition. You guys in the background can step in here anytime now. C'mon, Arthur, I KNOW you know what the wiring is.

I went back and did some researching. I did NOT use a voltage relay on the glow plug circuit. I mounted the glow plug relay timer on the driver's side fender well. I ran an eight gauge wire directly from the battery to the box. I used 4 of the 5 wires (the box was from a 300D) to power the glow plugs. I capped the remaining wire. I did not have a light for the glow plugs but the wiring is there if you want to connect the light. You need a feed from the ignition to activate the glow plugs.

The relay setup I was thinking of in my earlier post was for an electric fan which I used in place of the clutched fan.