I have a shift light that I am trying to install. The directions say to hook it up to the "tach line of the engine computer or from the switched side of an ignition coil". My question is what wire to hook it up to. I was going to use the wire that is going into the back of the tach. But there is a huge bundle of wires. Or I would not mind going from the switched side of an ignition coil, but what wire would I need to hook it up to, to do that?? thanks for your help.