Main Relay (Computer/Fuel System): Testing and Inspection

Fig. 73 Main Relay:

Fig. 72 Main Relay Pin Outs:

Relay Test

1. Remove the main relay, near the under-dash fuse box.
2. Attach the positive battery terminal to the #4 terminal and the negative battery terminal to the #8 terminal of the main relay. Then check for continuity between the #5 terminal and #7 terminal of the main relay.
a. If there is continuity, go to step 3.
b. If there is no continuity, replace the relay and retest.
3. Attach the positive battery terminal to the #5 terminal and the negative battery terminal to the #2 terminal of the main relay. Then check for continuity between the #1 terminal and the #3 terminal of the main relay.
a. If there is continuity, go to step 4.
b. If there is no continuity, replace the relay and retest.
4. Attach the positive battery terminal to the #3 terminal and the negative battery terminal to the #8 terminal of the main relay. Then check for continuity between the #5 terminal and the #7 terminal of the main relay.
a. If there is continuity, the relay is OK; If the fuel pump still does not work, go to HARNESS TEST.
b. If there is no continuity, replace the relay and retest.


Main Relay Harness Test

1. Keep the ignition switch in the OFF position.
2. Disconnect the main relay connector.
3. Check for continuity between the BLACK wire (2) in the connector and body ground.

Fig. 60 Harness Test Pins 1 And 2:

Fig. 61 Harness Test Pins 2 And 5:

4. Attach the positive probe of the voltmeter to the YELLOW/BLUE wire (1) and the negative probe to the BLACK wire (2).
a. Battery voltage should be available.
b. If there is no voltage, check the wiring between the battery and the main relay as well as #1 fuse (10 amp) in the under-hood relay box.
5. Attach the positive probe of the voltmeter to the BLACK/YELLOW wire (5) and the negative probe to the BLACK wire (2).
6. Turn the ignition switch ON.
a. Battery voltage should be available.
b. If there is no voltage, check the wiring from the ignition switch and the main relay as well as #1 fuse (15 amp).
7. Attach the positive probe of the voltmeter to the BLUE/RED wire (4) and the negative probe to the BLACK wire (2).

Fig. 62 Harness Test Pins 2 And 4:

Fig. 63 Harness Test For Fuel Pump Operation:

8. Turn the ignition switch to the START position.

a. Battery voltage should be available.
b. If there is no voltage, check the wiring between the ignition switch and the main relay as well as #10 (7.5 amp) fuse.
9. Connect a jumper wire between the BLACK/YELLOW wire (5) and YELLOW (7) wire.
10. Turn the ignition switch ON.
a. The fuel pump should work.
b. If the fuel pump does not work, check the wiring between the battery and the fuel pump, and the wiring from the fuel pump to the ground (BLACK wire.