Does anyone have any idea where an 80's ISSPRO tach sensor would be installed to read from? There is no tach wiring going to the IP or alternator, so I am at a loss as to where it would be reading from. The tach itself is lazy, so I'm thinking that it probably just needs a new sensor, but I am having trouble tracing the wiring as there is a big rats nest of gauge wiring and dealer A/C wiring.