I purchased a Sun #CP7901 that I can't get to work. I have a 69 Camaro with the coil on top of the distributor. The instructions say red to hot, black to ground, and green to the negative terminal that is located next to the terminal that actually starts the car. As you know both terminals are located on the side of the coil. I followed the instructions but my tach's working. I want to know can I tap one of the harness wires that plugs into coil near these terminals. One of them has to be a negative that flows back to the battery. Is this a common problem or do I have a busted tach?! Thanks.