I am hooking up a factory tach. The tach is labeled as to where the wires go (ground, 12v, coil). Where do I hook up the wire that goes to the coil? I have an 89 TBI. The coil is external to the cap. there are 2 connectors that snap on to the coil. I think there are 4 wires total. Anyone know which one I need to tap into?