Your tachometer in your 1985-1995 MR2 will not work with the Gen4 engine due to the Gen4's lack of distributor. This device converts the tachometer signal from the Gen4 engine to be compatible with the existing tachometer in any 85-95 MR2 or 86-99 Celica/Camry. This eliminates the old school need to dissasemble the instrument cluster to remove and re-solder a new resistor to the circuit board. Use our helpful diagram below to hook up your tach adapter to the Prime plug and play wiring harness. It couldn't be easier!