I have a 69 Torino that did not originally come with a tach, but a previous owner added a factory tach, which is not working. It has the correct tach lead, a red and a black two wire harness with a large firewall plug that connects under the dash. (it is connected... correctly?... I don't know yet, have not opened the dash) I want to start with the engine wiring. They spliced the red wire into the standard red/green coil (+) terminal. The Black wire has been cut, and is not attached to anything. The only wiring diagram I have at the moment is a jpeg I can't read the wiring colors on when I blow it up. I've not had a factory tach before and have no idea where the black wire needs to go.