Abiddle - I have an original GM accessory tach that came with my car and I'm the second owner of a 69 Camaro SS. My tach has the "GM" embossed logo, I am extremely confident this came with the car. I took it out years ago and shelved it but now being original to the car I am going to re-install it but I don't have the wiring diagram either. (blue, blk, orange, white) did you ever figure out the correct wiring?