85 300D glow plug relay intermittent no glow plug light - PeachParts Mercedes-Benz Forum

funola · #1 03-09-2014, 06:03 PM

This has been an intermittent problem since I bought the car 2 years ago. I estimate it happens less than 1 percent of the time. I have cleaned all the terminals on the glow plug relay and have added test light bulbs across the glow plugs and the violet wire so I can see at a glance whether they are getting power.

Today, it happened again. No cluster glow plug light and neither test light bulbs were lit with the key turned to the on position, which means the glow relay was not getting the trigger signal and thus no glow plug light.

I recycled the ign switch about 20 times which didn't help. I then cranked the starter for a second, recycled the ign switch to on and immediately got the glow light and both test light bulbs lit. Note: I did not touch the gear selector throughout this ordeal.

The problem is in the ign switch apparently. Is there an adjustment in the ign switch? Maybe if I get ambitious, I'll take apart the ign switch and give it a good cleaning.

Diesel911 · #2 03-09-2014, 09:54 PM

While it still was working good one of the Contact Points on My Ignition Switch was nearly gone.
See Post #13 for a pic of the contact which is circiled in the pic.
78 300d

PackerEdgerton · #3 07-19-2014, 12:42 AM

Hi Funola,

Hey I was reading your thread on glow plug problems and my symptoms are identical to yours (exactly!). Did you figure out what the problem was? If so, would you be kind enough to share?

Thanks,

Packman

funola · #4 07-19-2014, 11:59 AM

Packman,

I never did fix that glow relay because it wasn't worth it for me to spend a lot on time on it. I could probably fix it if I really wanted to. Instead, I made it into a manual system which is working great. You can read about it in this thread:
Unique manual glow plug control

PackerEdgerton · #5 07-19-2014, 01:51 PM

Thanks Funola,

That's a cool fix! Thanks for sharing.

Packman

Murkybenz · #6 07-19-2014, 04:38 PM

Reading your post the (cranked the starter for a second / and then lamp worked) jogged my memory.
I had similar and it was ONE worn alternator brush making intermittent contact.. Heres a link to a two page thread, second page with a picture will explain it easier.
I have had this issue on two e300d (1989/90) and both times no glow lamp or warning lamps just main battery lamp and Abs.
1995 E300D Glow plug issue.. Yes I've searched..

Zacharias · #7 07-20-2014, 04:14 AM

I had the identical problem last winter, right down to it working somtimes if I kicked over the starter motor. I too was convinced it must be the ignition switch.

Then for fun I popped the hood and fiddled with the connections at the relay. I pressed down hard on the small plug and CLICK on went the relay.

Drove that way, having to intermittently pop the hood and press down on the connector, for a couple of weeks until I got another relay.

Another local person on this forum had a similar issue with his SD, in colder weather, but in his case he had to tap the side of the relay to get it to engage.

I think I am going to go manual on my 300d one of these days.