After reading this thread I realized the GP light in my 87 was only staying on for 2-3 sec no matter how cold it got. I tested the relay with the purple wire pulled and it stayed on for 38 seconds. I swapped a spare 87 relay and sure enough the light was on much longer. After taking the bad relay apart I found a couple of bad capacitors. I'll replace those, clean the contact on the relay and report back. Its good to have a spare.

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CENSORED due to not family friendly words

First, this post-thread is closely related to this thread:
http://www.peachparts.com/shopforum/diesel-discussion/397328-35-cold-start-toronto-1985-mercedes-300d-original-engine-2.html

Second, this concerns my 1985 300CDT - W123 OM617.952 (California).

Third, I'm looking for help identifying the technical specifications for the 3 capacitors that are situated on the glow plug relay's circuit board.

From the outside of the glow plug relay unit's housing:
001-545-98-32
89 91 80
12V/5-Zyl.

I have extracted the unit and attached are three pictures.

I've used as strong a light and magnifying glass as I have to read the details on the capacitors but as I've notated on picture #1, I am having difficulty reading the details and deciphering them.

If anyone is able to help clarify the details of the capacitors, that would be great. Otherwise, baring not enough information about the capacitors, I'll reassemble the unit.

Thanks for any help with this.

Attached Thumbnails

     

All three are electrolytic capacitors, which are used for bypass filtering, almost never for timing purposes. ELectrolytics, unlike other types of capacitors go bad with time, just replace them if they're old. One of them is identified as 47 uf, which is its capacitance value. Just replace it with any electrolytic cap that's around 47 uf rated 24 V or above and you will be fine. The numbers on the other 2 does not look like capacitance values. Take closeup pics of the 2 caps and the markings, maybe I can tell.

A free source of electrolytic caps are old cell phone car chargers, LCD TV's etc

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85 300D turbo pristine w 157k when purchased 167,870 July 2025
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked

I've taken a bunch of pictures.
Here's the link to them:
https://imgur.com/a/MM3VAjw

> The "47" was easy to clearly photograph.
> The large blue one with the green lacquer was tougher.
> The really small black one on the corner next to the Texas Instruments chip is next to impossible to get clearly.

Anyway, best I could do for the moment.

Thanks again-

If the unit is working fine, leave it alone. If it is not, then try replacing the electrolytics and see if it helps. The big one with rubbed off numbers is about the same size as the 47 uf, so replace it with a 47 uf. The small one with rubbed off numbers, replace it with a 10 uf. The exact capacitance values for those 3 electrolytics are not critical IMO, as I said earlier, they are not for timing, i.e. control the duration of glow on/ off times.

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85 300D turbo pristine w 157k when purchased 167,870 July 2025
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked

Beautiful.
Sincere thanks for sharing your knowledge. Very helpful and new learning for me.