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Discussion Starter #1
Here's the scenario. Aftermarket tach, but original SS-style for a '71 SS. The only connectors it gets are from the HEI to the PIN connector, and then general power from the printed circuit. The cluster has a headlight ground, or rather the headlight switch is grounded. The tach used to flutter around, but then at night I pulled lights on and found no lights inside or out, and the two signals and hi-beams lit up. I discovered a screw not grounded on the circuit. I fixed this. Everything was working for a while, and then this would happen to the tach: I'd drive around for a while, and things would appear to be OK as far as accurate RPM reading and the tach not dancing everywhere. Suddenly during driving it would start to flutter between 2500-3000 RPM on the gauge, like around the 2nd-3rd gear shift. Since the car is a three-speed automatic, I think it only started to dance there since it was the last gear and no more RPM readings were sending to the gauge. Anyway, I found later that if I pulled the light knob out, whether for parking or all lights, the tach would not flutter and would remain consistant.

Can a ground do this? I thought it possibly could, but I'm not sure what kind of ground could do this, since the headlight switch is grounded properly.

I had a security system installed the yesterday and picked up my car today. I found now that the tach would not work with parking lights, only full lights, which made me think possibly a ground was moved or again, moved out of place. I'm just not sure if a ground is a ground and no matter if it's grounded completely or not if things will not work, as if there are certain degrees of malfunctioning that occur when things aren't grounded.

Does anyone have a clue as to what could be happening? Possible grounds to check out or anything?

Thanks in advance, I really appreciate it.
 

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Things to try:
Ground wire from battery (-) to the right inside fender.
Extra ground wire from tach to dash frame.
 

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Discussion Starter #3
Looking at my car, the ground wire goes from the negative on the battery to the junction block. Would that have any part or anything, or is a ground a ground? Also where on the right fender should it be grounded to, or is it on the fender eyebrow?
 
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