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

PURPOSE
Electronic Engine Control (EEC) power relays provide power to the Electronic Control Assembly (ECA). The power relays also provide reverse battery protection and increased load handling to improve ignition switch reliability.

CONSTRUCTION
There are two types of power relays:

Standard EEC Power Relay:

The Standard Power Relay; a single pole single throw (SPST) relay.
This relay consists of a movable contact in the normally open position and has an internal diode in series with the relay coil.

ISO EEC Power Relay:

The ISO power relay; a single pole double throw (SPDT) relay.
This relay does not have an internal diode and is used with a separate stand alone diode.

OPERATION
The EEC power relay is energized in "RUN" or "START" through the ignition switch. When energized, battery voltage (B+) flows through the relay. This voltage powers the ECA and its outputs.

When the ignition switch is turned "OFF", the relay de-energizes, stopping B+ to the ECA.