[Ben M.]

Originally Posted by T70GTO

any thoughts?

All of the '75-81 Trans Am tachs I've worked on have been 2 wire: +12V pink and coil is brown or white depending on year. The case is grounded through the cluster housing. Earlier ones may be different and require a separate ground lead that HPP is referencing.

[rexs73gto]

Correct the later ones 75+ are grounded through the cluster itself & then the lights are in the circuit board plus the later HEI units plug directly into the dist. so they only need the 2 wires to power them. The earlier ones 74- needed the extra ground to the coil for the power / ground source.