The other two leads on this connection are connected to a speed sensor that resides at the back of the A/9 assembly (compressor). When the compressor turns this sensor produces an AC voltage signal that is sent to the MAS unit telling it whether the compressor is Okee Dokee or if it is becoming Pokee! The generated signal should be >300 mV AC if not the sensor is weak. If the signal coming out is good than check to make sure it is getting to the MAS unit. If it is than you need to confirm that a few other signals are present at the MAS unit prior to investing in the replacement.