Not starting - PeachParts Mercedes-Benz Forum

mobenz · #1 07-23-2008, 04:35 PM

I apologize for the cross-post, but this isn't necessarily a diesel issue.

1978 300CD w/ Automatic transmission. Sloppy shifter linkage due to missing bushings. Has history of intermittently not "activating" the glow plugs or glow plug indicator light, which basically means the circuit isn't complete. Now, zero activity when I try to start it. Dash lights, even glow plug indicator, are on. When I put the ignition in the Start position, there isn't even a sound. I suspected the Neutral Safety switch, and have tried to test it, and even jump the wire to get the starter to spin, but that doesn't even work. I put a screwdriver across the posts on the starter and it spun, but didn't engage. I strongly suspect that I have dirty or worn contacts on the ignition switch. I can purchase the "electrical only portion", but I'd like to be a little more sure about the diagnosis before I do. Yes, I could take it to the shop, but half the fun of owning one of these beauties is being able to work on it myself, with the help of knowledgeable folks on the forum that is. If you have any suggestions, or further questions to help me track this booger down, I would be most grateful.

Diesel911 · #2 07-23-2008, 08:11 PM

It sounds like one of those push button remote starter switches would be handey. One end hooked to the (+) battery terminal and the other end hooked to the Starter Solenoid terminal that goes to the ignition switch.

Do a terminal block on the fender skirt in front of the battery?
Do you have the Loop Style Glow plugs or the pencile type?

mobenz · #3 07-23-2008, 09:31 PM

No terminal block on the fender. Loop style for now, but converting very soon to pencil type fast start. I will see about the switch for now. Is that terminal the one with the small wire?

Diesel911 · #4 07-24-2008, 01:26 AM

Quote:

Originally Posted by mobenz

No terminal block on the fender. Loop style for now, but converting very soon to pencil type fast start. I will see about the switch for now. Is that terminal the one with the small wire?

It will be a terminal with a small wire. I tried to look at the factory wiring diagram but it was not a lot of help.
The wiring diagram in the Haynes manual show the small wire as being Violet colored and it runs from the starter to the- Relay, Air Conditioning/Starter. At the Air Conditioning/starter relay and branching from the same terminal a Violet wire also goes to the Pre Glow Time Relay.

Somewhere on the AC/Starter relay is a Violet/White wire that goes to the Ignition switch.
The other 4 wires going to the Starter are all Red and go to the same terminal on the starter (instead of the fender terminal block).

300sdlguy · #5 07-27-2008, 08:01 PM

Can you do this with a 300SDL. I just purchased one that has been sitting several months, and it is doing the EXACT same thing: no start, tried to jump starter, but is simply spin's without engaging.

Oracle12345 · #6 07-27-2008, 09:53 PM

INTERLOCK switch???

sounds like a interlock switch problem to me. Replace your interlock switch and your problems should go away. The interlock switch bolts to the side of transmission, held on by 4 10mm bolts

300sdlguy · #7 07-27-2008, 10:06 PM

THANKS, I will check into that. Also I noticed that when I turned the key on there was slight smoke coming from the glow-plug relay, is this related? Also, the battery keeps draining itself could the interlock switch be causing this?

Oracle12345 · #8 07-27-2008, 10:18 PM

interlock shouldnt cause a battery drain. Something else that is always hot is draining the battery. Look at the wiring diagrams and see whats always hot. You could also isolate the drain problem by pulling each fuse until the battery stops draining. Once you pull a fuse that stops draining the battery then you have found the problematic areas.

Smoke from your glow plug relay isnt good. You may have to replace your glow plug relay. You may have shorted your glow plug relay and it is draining your battery since its always hot.