[spudder]

I'm in the process of installing a tach from a larger GMC truck in a '65 C10. I've pretty well got the installation figured out, but the wiring has me a little confused. Most every tach I've encountered has two wires for the tach to function. 12 volt power and another that goes to the - terminal on the distributor or tach terminal on HEI.
This tach is secured in the can by 3 studs with only 1 stud being insulated from the case and no spade terminals for the wires.
The case is stamped AC Div. GMC. I know the tach came out 0f a '70s-''80s big GMC gas burner.
Anyone know anything about this style tach?
Any help appreciated!
Just looked at the tach and found a date October 13,1977