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Jumping Dashboard Indicators & Mystery Cable on 74 tii


hynrgee

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Several months ago I had a new alternator bracket installed along with an upgraded starter (a Bosch SR441X). I almost immediately noticed that what were previously stable dashboard indicators were jumpy. In particular, the temperature gauge seemed most jumpy perhaps steadying the most as I accelerated. Nothing else was affected and the car has been driving as strong as ever. A couple of weeks ago I noticed that one of the fog lights would not turn on consistently. The reading on this site indicated a faulty ground could explain both conditions. Since then I have been tracing wires and tightening screws or securing connections as I could. While I no longer have problems with the intermittent fog light and the jumpiness has settled down, it is not completely gone. Earlier today I located a black wire that was not connected to anything. I am attaching two photographs. The first shows the black wire and the connecter type while the second photograph shows where the black wire leads (into darkness). I have yet to track it all the way as I may have to jack the car up to see where the wire leads. Meantime, does anyone have any ideas based on these two photographs? Would it be safe to just ground the black wire?

 

Note that the photographs are fairly high resolution and I have labeled what I could in red. It may be necessary to zoom in on the images to see that I am using electrical tape to prevent the wire from sinking back into the engine bay. 

 

post-47311-0-91692900-1421741179_thumb.j

 

This second photograph shows that the black wire leads under the dip stick and appears to connect to the ZF - Gemmer - Lunkung Friedrichshafen AG part. I have no idea what that is or if it could help to explain what is happening. 

 

post-47311-0-91354400-1421742568_thumb.j

 

Any suggestions are appreciated.

 

Thanks.

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There are a few grounds that could effect the fuel gauge, but the one that I've found most suspect is under the voltage regulator (thick brown).  The sheet metal screw that anchors the VR and the ground is screwed into the inner fender.  That screw/fender connection gets corroded, creating a poor ground.  I've cleaned the whole area to bare metal and replaced with a throughbolt.  Solved my jumpy fuel gauge.

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Thanks guys...in case it makes any difference a prior owner left the backup light switch off and that's one of the fixes I had made at the same time that the alternator bracket was replaced and the starter updated. I'll see if I can locate the brown ground that you mention, Paul. Since the old alternator is still on the car the thought that it wasn't reconnected completely has crossed my mind so I will be checking those connections, too. I guess I won't go surfing after all.

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As I popped open the hood to my tii and grabbed some tools my next door neighbor came by. He's a 32 year wrencher who is teaching transmissions and AC at a technical school. He thought I might be interested in EuroSunday at the Cal Auto Museum. After chatting a bit I told him about the jumpy temperature gauge. He immediately sought out the water temperature sender, located it, pulled gently on the crimped male connector that attaches to the sender, and said "wow". He tells me I have a very tenuous connection between the crimped female head on the cable and the male lead on the sender. He suggests that rather than search for loose grounds that I begin by cleaning the grease off the sender, pulling the insulation off the wire, exchanging the old crimped head with a new one, soldering the cable to the new head, reattaching everything, and going for a drive to see if the jumpiness of the gauges continues.

 

I did as he said, perhaps a 30 minute job, and then take a drive. The gauges were very stable. Absolutely no jumpiness. Everything was working as I recalled it was working previously. On the way home I stopped at BevMo to pick up a nice bottle of wine for my neighbor. It was the least I could do as he probably saved me several hours as well as frustration.

 

As to the mysterious black cable, it is still a mystery. I applied a circuit tester today and determined that it's a live wire.  The sleuthing will continue on some future date. For now I am very satisfied as my concern with the temperature gauge was as much about its accuracy as the jumpiness itself. Very relieved to see it steady at just below center as it was before. I'm sharing this solution because, in retrospect, it seems so obvious that it was easy to miss.

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