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

The MPI Control Relay supplies power to the fuel pump drive terminal.

When the ignition switch is turned to the ON position, voltage passes through the Inhibitor Switch to the Control Relay. The relay closes and power is supplied to the fuel pump drive terminal. Once the engine is running, the fuel pump 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 power supply by opening the MPI Control Relay 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.