I have a tachometer and would like to install it on a 1998 Toyota Corolla. The instructions shows one wire to power supply , one wire to instrumentation panel lights and the last wire to the coil to pick up a negative signal. The 1998 corolla is set up with a dual module coil system.

My question is how do you hook up a tachometer, when the coil consist of is a dual coil system?? In other words there are two 4 wire harness to two individual coils. Each wire harness has 4 wires which plug into one of the coil modules. Does anyone have any suggestions as to how to hook up this external mount tachometer???