GM Service Manual Online
For 1990-2009 cars only

Turn Signals

During turn signal operation, power is supplied from the TURN fuse in the IP fuse block when the ignition switch is in the RUN or the START position. Power is supplied to CKT 139 (PNK) to the normally closed TURN fuse contacts of the hazard switch through CKT 1508 (LT BLU) to the turn signal flasher. From the turn signal flasher current flows through CKT 1697 (PPL) to the turn signal switch. When the turn signal switch is in the LEFT TURN position, voltage is supplied to the LT TURN (front) fuse via CKT 1414 (LT BLU/WHT) and to the LT TRN (rear) fuse via CKT 1418 (YEL/BLK). The LT TURN fuse supplies power to terminal A of the LH park and turn signal lamp and the LH side marker lamp via CKT 2114 (LT BLU). The LT TRN fuse supplies power to terminal A of the LH rear park and turn signal lamp via CKT 618 (YEL). The LH park and turn signal lamp receives ground through CKT 150 (BLK) to G111. The LH rear park and turn signal lamp receives ground through CKT 1350 (BLK) to G450. The LH side marker lamp receives ground from CKT 2309 through terminal B of the LH park and turn signal lamp to G111, via CKT 150 (BLK).

When the turn signal switch is in the RIGHT TURN position, voltage is supplied to the RT TURN (front) fuse via CKT 1415 (DK BLU/WHT) and to the RT TRN (rear) fuse via CKT 1419 (DK GRN/WHT). The RT TURN fuse supplies power to terminal A of the RH park and turn signal lamp and the RH side marker lamp via CKT 2114 (DK BLU). The RT TRN fuse supplies power to terminal A of the RH rear park and turn signal lamp via CKT 619 (DK GRN). The RH park and turn signal lamp receives ground through CKT 250 (BLK) to G112. and the RH rear park and turn signal lamp receives ground through CKT 1350 (BLK) to G450. The RH side marker lamp receives ground from CKT 2309 through terminal B of the RH park and turn signal lamp to G112 via CKT 250 (BLK). The park side of the front park and turn signal lamps do not illuminate due to the voltage drop across the side marker lamps. During operation, the lamps illuminate immediately. The lamps begin to flash when the current flow heats the timing element in the flasher and repeatedly opens and closes the circuit.

Hazard Lamps

During hazard operation, power is supplied from the HAZ LP fuse in the underhood fuse block that is hot at all times through CKT 149 (ORN) to the HAZ LP fuse contact of the turn signal switch. When the hazard switch is activated, power is routed to the turn signal lamp flasher via CKT 1696 (GRY). From the turn signal flasher, current flows through CKT 1697 (PPL) back to the turn signal switch's now closed hazard contacts to the following circuits for LH and RH turn signal operation:

    • CKT 1414 (LT BLU/WHT)
    • CKT 1418 (YEL/BLK)
    • CKT 1415 (DK BLU/WHT)
    • CKT 1419 (DK GRN/WHT)

Park, Side Marker and Rear License Lamps

For park/marker operation, power is supplied from the PARK LP fuse through CKT 240 (ORN) to terminal F7 of the body relay block where power is fed to the following components:

    • The headlamp switch
    • The park lamp relay coil
    • The load side of the relay contacts

For automatic operation, the body control module (BCM) grounds the park lamp relay coil to feed CKT 74 (LT BLU) during auto headlamp operation. When the headlamp switch is in the PARK or HEAD position, current flows through CKT 74 (LT BLU) to the underhood fuse block. The current feeds the following fuses:

    • The FR PRK fuse
    • The LR PRK fuse
    • The RR PRK fuse
    • The TRL PRK fuse (Utility)

The FR PRK fuse supplies power to the park side of the RH and LH park and turn signal lamps. The FR PRK fuse supplies power to the LH and RH front side marker lamps terminal A. During normal operation, when the park lamps and the turn signals are turned ON, voltage would be applied to both terminals of the front side marker lamp when the turn signal lamp flashes ON. When this action occurs, the side marker lamp turns OFF. When the turn signal lamp turns OFF, the side marker lamp will illuminate again. The LR PRK fuse feeds CKT 2509 (BRN) which supplies voltage to the LH rear park and turn signal lamps. On the pickup, CKT 2509 (BRN) also supplies voltage to the LH rear license plate lamps and the LH rear side marker lamps. On the utility, the LH rear park and turn signal lamps are grounded to G450 via CKT 1350 (BLK). On the pickup, the LH rear park and turn signal lamp, LH rear license plate lamps and the LH rear side marker lamps are grounded to G475 via CKT 1750 (BLK). The RR PRK fuse feeds CKT 2609 (BRN/WHT) which supplies voltage to the RH rear park and turn signal lamps. On the pickup, CKT 2609 (BRN/WHT) also supplies voltage to the RH rear license plate lamps and the RH rear side marker lamps. On the utility, the RH rear park and turn signal lamps are grounded to G450 via CKT 1350 (BLK). On the pickup, the RH rear park and turn signal lamp, RH rear license plate lamps and the RH rear side marker lamps are grounded to G422 via CKT 2250 (BLK). The TRL PRK fuse (utility only) supplies power to CKT 2109 (BRN) which feeds the LH and RH rear license plate lamps. The lamps are grounded to G402 via CKT 1650 (BLK). When the park lamp switch is in the PARK position, the daytime running lights are ON when the ambient light sensor senses daylight, and the headlights will be ON when the ambient light sensor senses darkness.

Stop Lamps

Pickup

During stop lamp operation, power is supplied from the STOP LP fuse in the underhood fuse block through CKT 1540 (ORN) to the TCC/stop lamp switch. When the brake is depressed, the contacts of the TCC/stop lamp switch close, routing power to CKT 17 (WHT). CKT 17 supplies power to the VECHMSL fuse and the high mount stop lamp relay coil. Current flows from the VECHMSL fuse through CKT 1320 (LT BLU) to the dome and high mount stop lamp. The ground is provided by G202 through CKT 1850 (BLK). The high mount stop lamp relay coil is grounded through CKT 350 (BLK) to G102, which energizes the relay. When the high mount stop lamp relay is energized, current flows through CKT 895 (YEL) to the turn signal switch. Current then flows to CKT 1418 (YEL/BLK) and CKT 1419 (DK GRN/WHT). CKT 1418 (YEL/BLK) supplies power to the LT TRN (rear) fuse, which feeds the LH rear park and turn signal lamp terminal  A, through CKT 618 (YEL). Ground is provided by CKT 1750 (BLK) to G475. CKT 1419 (GRN/WHT) supplies power to the RT TRN (rear) fuse, which feeds the RH rear park and turn signal lamp terminal A, through CKT 619 (DK GRN). Ground is provided by CKT 2250 (BLK) to G422. When the left or right turn signal is turned ON, the appropriate turn signal will flash. The opposite side will remain ON in order to serve as a stop lamp when the brakes are applied.

Utility

During stop lamp operation, power is supplied from the STOP LP fuse in the underhood fuse block through CKT 1540 (ORN) to the TCC/stop lamp switch. When the brake is depressed, the contacts of the TCC/stop lamp switch close, routing power to CKT 17 (WHT). CKT 17 supplies power to both the VECHMSL fuse and the stop switch contact of the hazard switch. From the VECHMSL fuse, current flows through CKT 1320 (LT BLU) to the high mount stop lamp and high mount stop lamp resistor. The ground is provided by G450 through CKT 1350 (BLK). From the stop switch contacts of the hazard switch, current flows through the turn signal switch to CKT 1418 (YEL/BLK) and CKT 1419 (DK GRN/WHT). CKT 1418 (YEL/BLK) supplies power to the LT TRN (rear) fuse (which feeds the LH rear park and turn signal lamp terminal A) through CKT 618 (YEL). Ground is provided by CKT 1350 (BLK) to G450. CKT 1419 (GRN/WHT) supplies power to the RT TRN (rear) fuse (which feeds the RH rear park and turn signal lamp terminal A) through CKT 619 (DK GRN). Ground is provided by CKT 1350 (BLK) to G450. When the left or right turn signal is turned ON, the appropriate turn signal will flash. The opposite side will remain ON in order to serve as a stop lamp when the brakes are applied.