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Why dose'nt my tach work?


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i just installed a factory tach in my 72 GS. Hooked a wire from the neg of the coil and nothing. Does it need to be grounded, if theres something wrong with the tach how do i fix it? anyone have any suggestions?

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Wiring diagram shows the tach to have a ground wire. It has been many years since the tach was installed in my GS, but I believe there were 3 wires. One for the coil, one for the ground, and one for power from the fuse block for illumination.

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This is a long shot, but some tach's don't work if you have the Pertronix ignition upgrade. If you have the Pertronix it could be that.

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the black wire from the tach needs to be attached to the frame of your car someplace where a good connection will be made, this is the ground. The red wire needs to be connected to your fuse block (perferably to a wire that is only on when the igntion is on.) The third wire, a green wire needs to be ran to the "tach" output on your coil, OR it needs to be ran to the negative out on the coil.

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