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  #1  
Old 07-31-2008, 01:37 PM
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Join Date: Jul 2007
Location: Huntsville, AL
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need help troubleshooting a dead gauge

I recently finished swapping a 617.952 engine into my 300D (Euro car, originally 617.912). On driving the car again, I immediately noticed that my temp gauge was dead. Prior to pulling the old engine it was working fine.

I've tried swapping the sending unit with the one from the old engine, as well as hooking up a spare instrument cluster, which I'm pretty sure had a working temp gauge in it. No joy. So I figure the only thing left is an open between the sender and gauge. Since I don't know which pin on the connector at the instrument cluster goes to the temp sender, I tested all 15 holes in the connector...no continuity anywhere. (That is, continuity between the holes and the push-on plug at the sender.) One of those little holes should have continuity with the sender plug, shouldn't it?

I worked the sender lead out of the engine wiring harness, going back about 18 inches or so. I thought I could have damaged the wire during reinstallation of the engine harness. But the wire looked perfect to me.

Does anybody have any tips for locating the break? The wiring harness goes into a black box on the inner fender that I assume is the glow plug relay, but that's just a guess. Anyway, I have no idea how to trace the sender lead past this point. Any help appreciated.

thanks,
Bruce
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1995 E300 200k
1981 300GD unknown km
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  #2  
Old 07-31-2008, 05:08 PM
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Do a search for your car's wiring diagram.
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Old 07-31-2008, 08:54 PM
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Thanks for the response. I'm looking at the wiring diagram in my Haynes manual...it looks like pin 2 on the instrument connector goes to the temp sending unit lead. Pin 5 looks like power to the gauge. Other than that, I'm not getting much out of it.
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  #4  
Old 07-31-2008, 11:10 PM
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Lightbulb found it

There's a push-connector for the temp sender wire in the left inner fender, behind the headlights and just below that relay box I mentioned. Somehow I had managed to pull that connection apart during the engine swap. That's all it was.

It was hard to recognize that connector as belonging to the temp sender because the lead at the engine side is a green wire. On my car, just before it emerges from the sheathed bundle at the other end, it becomes a black wire. I don't know if this is standard or not.

Just got back from test driving the car; those 40 extra ponies feel mighty fine.
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