Hmmmm, after reading some posts, I have a question about my 83 300 SD glow plug system.
I have the later model AFTERGLOW timer/relay, and to my understanding I should not get the FULL burn when my engine is hot.
When starting my car cold or hot, the plugs run for a very long time. This does not bother me on the cold starts but on the hot?
I run through a LOT of glow plugs, I mean every month or so I have to replace them. I have a hunch they are running when they shouldn't be.
I have changed engines (not for this reason ), and the problem continues. I have replaced the timer unit and the problem continues. What gives? Is there a broken signal wire? a bad temperature sending unit? I do not have the diagram for this system. Where does the signal come from? I am tired of buying so many damn glow plugs! It is especially bad when I discover 2 have suddenly burned out on one of those -40 F mornings.
Should I find a new harness?
I haven't driven the car in months, but with the interior restoration completion date coming soon along with another summit county winter I would like to resolve this problem. (Did I mention I am tired of laying down 50 bucks every month? )

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1983 Mercedes 300SD
1987 Mercedes 300SDL
2001 VW Passat 2.8 AWD
2007 OM642 Jeep WK 4x4