Hi Pete, I have a 1966 GTO with a factory tachometer that does not work. When I got the car, the previous owner had a Chevrolet engine in it. I have installed a Pontiac engine. I purchased the AMES tachometer wiring harness M11095 kit. I connected it to the negative coil and feed it through the firewall to connect the the male brown wire plug to the tachometer female brown wire plug. The tachometer lamp bulb works so it is getting power through the wiring harness. Can you share any thoughts from your vast experience on what the problem is ?