Main Relay (Computer/Fuel System): Description and Operation

The MPI Control Relay is a multi-purpose relay that switches power to the vehicles sensors and actuators
When the ignition is turned ON, power from the Control Relay energizes the injector coils, the Air Flow Sensor, and the Idle Speed Control Servo.
When the ignition switch is turned to the START position voltage passes through the Inhibitor Switch to the Control Relay. The relay closes the circuit to the fuel pump drive terminal. Once the engine is running, the fuel pump drive terminal will be taken over and controlled by the MPI Control Unit.

In the event of an engine stall or other abnormal condition, the Control Unit will interrupt fuel pump drive terminal power circuit.

NOTE: Failure of the Control Relay prevents power supply to the fuel pump, injectors and/or the MPI Control Unit, resulting in a start failure or engine stalling.