Help with 350SDL glow plug wiring - PeachParts Mercedes-Benz Forum

old goat · #1 10-21-2009, 01:41 PM

My glow plug relay on the 300SDL is going bad so I decided to replace it with the unit used on the 350SDL and 350SD which has after glow. The problems I did not consider are two fold. First off I have the 350SDL wiring diagram but it does not identify which wires are attached to which pins on the smaller 5 pin plug. The plug IDs are 50, 31, 15, LA and T. Does anyone have that information available? I need either the wiring color code to each pin or the identification of the device each wire comes from.

The second problem is that I would love to find one of the 5 pin plugs so the installation is clean. I am more than willing to buy the plug unit and pay for shipping. I figure someone out there has one from one of the later 603 installations.

Thanks a ton!

NJ300sdl · #2 10-22-2009, 04:42 AM

3.0 and 3.5 have different part numbers for glow plugs. You may have to change them also.

old goat · #3 10-22-2009, 07:43 AM

Thanks. You are right. Now the question is why?? If it has to do with longevity because of the afterglow, then I can stick with the ones I have as they have maybe 10K on them. Comparing the pictures of both years, the plug appear to be the same in size and length. Does anyone out there know why they are different part numbers?

Thanks

compu_85 · #4 10-22-2009, 07:48 AM

350s have a differently shaped prechamber.

-J

old goat · #5 10-22-2009, 07:54 AM

Thank you. That makes sense and would suggest I can just stick with the current units and change to the new relay without issues, well other than re-wiring and finding a 5 pin plug.

sneezlsrus · #6 10-22-2009, 08:58 AM

I have a 91 350 sdl that blew the original engine-I put an earlier engine in and the only way it would work was to use the afterglow plugs with the afterglow relay- my glow light wouldn't come on until I did- I updated the system totally and it starts great- also I am told the old style plugs don't have a great life span when used with afterglow- I can't verify this. Brian

old goat · #7 10-22-2009, 09:13 AM

Thanks Brian. I will have to see what happens. I thought perhaps longevity was the issue. I have asked the question of Beru but do not have a response yet.

Frank

babymog · #8 10-22-2009, 10:53 PM

You will want the glow plugs for a 300D 2.5 turbo ('90-'93 300D / 602 turbo) or the 1987 190D 2.5 Turbo. The 2.5 did not have the angled-injection and different prechambers of the 3.5L, but it did have afterglow.

old goat · #9 10-23-2009, 07:04 AM

Thanks for that information. I will keep that in mind for the next set of plugs. The current units are not very old so will hold up for a while. I will just have to keep an eye on them and periodically measure resistance. I had thought a little about those 2.5 plugs but was not sure about their use so your information is greatly appreciated!

Frank