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