OM617 W123 Glow plug power source? (low voltage at relay) - PeachParts Mercedes-Benz Forum

Jarod · #1 12-06-2014, 04:07 PM

Hi again!
Sooner or later I'm sure you guys will get sick of me asking dumb questions.

But until then, here's a dumb question:

The 1982 W123 300d I picked up for my wife to drive, the one that I had tie rod and steering issues that were all my fault...

A new issue has cropped up, I think its been an issue all along, but I didn't notice how hard it starts during the warm weather.

I replaced all 5 glow plugs when I got the car at the beginning of the year, replaced the primer pump and that made the car start great all summer long, no air in the fuel, and 5 working glow plugs.

However the other day, it wouldn't start at all. I checked the glow plugs, all less than 8 months old, ohmed out ok (I know thats not a for sure test)

I then checked the voltage at the relay. 12.3 key off, 9.1 key on. battery is good, battery voltage drops from 12.3 to 11.9 when the key is on, cranks very fast.
The entire fuse panel also drops to 9v when the key is on.

I figure this is the glow systems draw that drops the voltage, but i think there must be a bad connection or possibly a cut wire somewhere.

The thick wire that goes to the fuse in the glow plug relay looks fine where I can see it, but where does it go?

Is there some kind of regulator or place that the relay and fuse box get the power from?

I pulled the kick shield thing off the dash on the drivers side, looked around in there, massive ratsnest of wires, couldn't find the big wire coming from the glow plug relay though.

EDIT: Doing some reading, I hear talk of an OVP fuse/relay near the glove box that might be related, the tach is kinda wonky, bounces around at idle, drops to 0 as soon as rpm is above idle. possible connection?

Where does the wire go? Why would the voltage be so low?
Will I ever stop having silly problems with my cars? Find out after a few people reply.

Thanks for any help in advance!
Tom