Glow Plug Component Location - W123
 

Howdy,

I'm trying to diagnose a problem with the glow plugs on my folk's 12/84 300D-T. Symptoms are no glow plug lamp and hard starting.

I've read the procedures in the archives for testing the glow plugs but I'm totally clueless as to where some of the components are located, specifically:

Glow plug relay

Glow plug harness connector (the one that is disconnected to measure resistance of the glow plugs)

80A Fuse


The process seems pretty straightforward, but I gotta know where to start :D

I plan to start with the resistance check then check for voltage at each glow plug connector. Sound reasonable?

Thank you!

Jim

Look for a plastic box on the drivers side, inside the engine compartment, near the headlight area, mounted on the inner fender.

Take off the cover, there will be a fuse inside. It doesn't look like a fuse, but more like a bar of metal with a screw on each side.

If it is blown, it will be obvious, because it will now look like just two screws with some metal underneath!

This location of the glow plug stuff (relays, wires, fuse, etc.) is at least good for a 80 or 81 car, don't know about yours...

240 Ed covered it well, but I can point out something additional. The bar fuse he talked about will sometimes look good, but have a fine crack at the edge from vibration. Remove the screws and see that the fuse is solid.

If it is in good shape, use a voltmeter at that fuse to see that there is voltage at the fuse when you turn on the ignition.

Also, check continuity of the number one glow plug. It serves as a temperature sensor by its current being measured by the glow plug relay.

Also use your voltmeter to see if there is voltage on the gp's. If there is, you should replace ALL FIVE glow plugs whether they have continuity or not.

Good luck,

I would also look closely at the fuse. For example, my was perfectly in tact, but it was bent downward in the middle. Someone on the forum here mentioned that and whoa....that was the entire problem. At 30 cents apiece, it was a nice fix :)

Don

saved my duppie ....
 

thank you diesel don. out of nowhere my 83 300dt lost glow plug light and evidentally the glow plugs as it would not start. did a search. ran across diesel don's note that the fuse can look good and still be at fault. i too had the bent down condition in the middle of the fuse as described by diesel don. took a fuse from another in the stable and all was cured. incidentally, the fuze broke in two upon initial removal. purchased two new fuses at local dealer. asked if i would get out with a charge of less than a dollar and was told no. $2.28 a piece. mentioned that i thought each was around 30 cents. parts man gave me a break. total for two - $2.28. again thanks to diesel don and the site in general.