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Tach stopped working

ord27

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I have an aftermarket tach for a non ralley 1970 Coronet dash.
It suddenly stopped reading signal.
I connected it under the hood....coil, positive battery post, and still got no reading. I then added a ground wire from the light socket metal tab to the negative battery post. It worked like a charm.

Question; how should I fix this in the dash?
I bypassed the amp meter by soldering those leads together. The amp meter posts are bare. Do you think things would work if I connected one of those posts to ground?

thanks in advance

tach back.jpg
 
The cluster unit itself grounds to the dash frame and the frame grounds to the body...
 
I figured as much, but something is amiss
 
yes. I have it hooked up to the negative side. That's what confuses me about having to run the extra ground wire
 
Does everything else work in the cluster lights etc
 
yes
tach worked for a while
 
Negative to the coil is not the same as a ground to the firewall....two different terminations...electrically different.
 
Negative to the coil is not the same as a ground to the firewall....two different terminations...electrically different.
Glad you responded mine would have been blunt
 
Last edited:
It sure sounds like you have a bad ground wire. Either the one grounding the gage cluster to the dash frame OR the dash frame to the body (short black wire with two loops, right side of steering column bracket, about 5" long I believe).

If worse came to worse, you could always run a ground wire from that bulb socket to the stud for the dash frame/body ground as mentioned above....worst case.
 
do I need to avoid grounding from the metal of the circuit board? or is that the point?
 
Just asking.
Shouldn't the phrase "return" be used versus "grounding"?

A ground wire is normally the green wire in household circuits, and the black and white wires are the "supply" and "return".
 
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