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JAH11's 1968 GTO

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Tach to HEI hookup

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The cluster's main electrical harness distributes power to the gages and lights via a plastic circuit board similar to what I have shown below. It's usually on the very back of the cluster. 

Once you install the tach in the cluster and its connections mesh with those in the black receiver, then the circuit board should go on the back of it and distribute the power and power up the tach for lights, 12V, and ground. Obviously the tach signal was to come from somewhere else, which you said you've established.



If you wiring is cut up behind the dash, let us know.

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  • 2 weeks later...

Here is the wiring diagram for a 70-71 GTO. While this is not the same as your 73, the wiring should be similar.


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Correct - the tach output from the HEI should match the stock, non-HEI wiring. Your 73 Grand Am is based on the Colonade style of A-body cars. Pontiac used, essentially the same dash and gauges in the Lemans/GTO/Grand Am body from 73-77. I am not aware of any gauge/wiring modifications they did just for the introduction of HEI.

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You're right. Sorry about that.


Here is the uber simplistic wiring diagram. I would remove the tach from the cluster and look at the back of the actual gauge. It should have some sort of markings for each electrode. Essentially the "green" wire is the signal/pulse line from the coil to the tach gauge. Black is ground. White a 12V light source or bulb, and red is the switched 12V source for the gauge.


Edited by Frosty
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