The green wire on the box is the tach output for an aftermarket tach. In the goodie bag that comes with the HI6 there should be an adaptor plug that plugs into the green wire, which is where you splice in the shiftlight and/or tach. If you don't have an aftermarket tach, it isn't necessary to use the green wire at all (unless you have a shiftlight) you can just run the wires that went to the coil originally and run them into the red and white wires on the HI6, they will return to the coil through the black and orange ones. This way all factory gauges, etc, should continue to work normal. Or you can run your aftermarket tach off the coil like I did, in roughly the same manner. Directly at the coil is the most accurate place, although I think I trust this ignition to be right on too. Fear not, it's all in the scematic you'll see when you read the distructions.