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

Three relays (main relay, cold start relay, and pump relay), and a diode unit are mounted on the engine rear bulkhead next to the vehicle battery. When the ignition key is turned on, the main relay is activated, connecting the battery circuit to the ballast resistors and the injectors. The relay also allows current to flow to the ECU and the pump switch on the air-flow meter. When the engine is cranked for starting, the diode unit is activated and thus energizes the auxiliary air valve, the cold start system and the fuel pump.