Traqmate Shift light indicator
 

I'm giving serious thought to purchasing the Traqmate shift light indicator. There are several ways to connect the unit to the car, but one seems highly preferable to me. That is to connect to the output of the ECU with the tach signal that is used for the tachometer in the dash. My car is a 95 M3

There are four wires going to the instrument panel from the ECU. Does anyone know which color combination is the tach signal? A knowledgeable person can save me a lot of time experimenting.