After doing a search on this site I used the guidance and performed a resistance test on the glow plugs of my '80 300SD Turbodiesel. When you first start the engine it runs a little rought but smooths out fairly quickly. Since the car is new to me I have been doing a fair amount of preventative maintenance.

To do the resistance test I removed the glow plug cable connector from the GP relay on the left fender well of the engine compartment. The plug has eight pin holes but only seven are actually in use. Since the engine only has five glow plugs I needed to determine which holes went with which GP. For future reference here were my findings:

#1 hole = GP#5
#2 hole = GP#1
#3 hole = GP#2
#4 hole = open
#5 hole = GP#3
#6 hole = ??
#7 hole = GP#4
#8 hole = ??

According to the earlier posts the main point is that all the glow plugs should have about the same resistance - around 0.5 Ohm. Using a digital ohm meter I connected the ground lead to the engine and the other lead one at a time to the holes in the connector. If any of the glow plugs reads significantly different from the others, it should be replaced. In my case the readings were as follows:

GP#1 = open/no reading
GP#2 = .4
GP#3 = .4
GP#4 = .4
GP#5 = .3

I have ordered a new glow plug for #1 and some other needed items today from FastLane. Hope this helps others to check their glow plugs

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• 2001 E320

I tested by 85 300td yesterday. I got between 1.5--1.7 ohms on all. I assumed that was within spec. Any comments?
There were only 5 metal connectors in my plug relay connection so I can't help you on what is the case with yours.

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1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13

Crowe,

If you have one open GP, your GP indicator (dash light) should flash after starting your engine. This is a built in test to notify you of any bad GP. Maybe yours doesn't work.

You have the procedure correct. One more thing I would test is the resistance between the cable connector and the terminal nut on the GP showing open just to make sure it isn't a bad wire in the cable or open connection to the GP. This resistance should be almost zero.

P E H

The dash light does not indicate any problem. It appears to work normally, coming on for a few seconds then going off. It does not flash, however it has come back on briefly a few times while the car is being driven. I have another post seeking an answer about why the light and buzzer would come back on occasionally while the car is being driven. The feedback was to check the ground of the gage cluster and the glow plug relay.

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• 2001 E320