67 68 Mustang Dash Tach Wiring
 

I am swapping to a factory GT instrument cluster with a 6K Tach for my 67 Fastback. The tach has two wires coming out of the back. Red and Black. Where do they connect? I would imagine one to the negative side of the coil and the other to ground maybe??? These things aren't cheap and I really don't want to fry it and the factory shop manual is no help on this one. Thanks