The exterior lighting system consist of the following lamps:

On vehicles with daytime running lamps (DRL), the HEADLAMP fuse in the underhood fuse block, supplies battery positive voltage to the headlamp switch. With the headlamp switch in the HEADLAMP position, battery positive voltage is supplied to the headlamp dimmer switch. With the headlamp dimmer switch in the LOW BEAM position, the headlamps dimmer switch supplies battery positive voltage to the normally closed switch side of the DRL relay. The circuit continues to both low beam headlamps. With the headlamp dimmer switch in the HIGH BEAM position, battery positive voltage is supplied directly to both high beam headlamps. Both low and high beam headlamps are grounded at G202.

On vehicles without DRL, the HEADLAMP fuse in the underhood fuse block supplies battery positive voltage to the headlamp switch. With the headlamp switch in the HEADLAMP position, battery positive voltage is supplied to the headlamp dimmer switch. With the headlamp dimmer switch in the LOW BEAM position, the headlamps dimmer switch supplies battery positive voltage directly to the low beam headlamps. With the headlamp dimmer switch in the HIGH BEAM position, battery positive voltage is supplied directly to the high beam headlamps. Both low and high beam headlamps are grounded at G202.

The DRL fuse in the I/P fuse block, supplies battery positive voltage to the normally open switch side of the DRL relay, through the DRL diode. The DRL diode drops the amount of voltage going to the DRL relay. The GAGES fuse in the I/P fuse block, supplies Ignition voltage to the coil side of the DRL relay. The daytime running lamps (DRL) will operate with the ignition ON, the headlamp switch OFF, and with the park brake disengaged. The DRL will illuminate the low beam headlamps at a reduced intensity. The DRL module supplies ground to the coil side of the DRL relay. This activates the DRL relay which supplies a reduced voltage to the low beam headlamps. Both headlamps are grounded at G202.

The PARK fuse in the I/P fuse block, provides battery positive voltage to the headlamp switch. When the headlamp switch is placed in the PARK or HEADLAMP position, battery positive voltage is supplied to the RIGHT HAND PARK LAMP fuse and the LEFT HAND PARK LAMP fuse in the I/P fuse block. The RIGHT HAND PARK LAMP fuse and the LEFT HAND PARK LAMP fuse supply battery positive voltage to the park lamps, tail lamps, and the body builder connector. The park and tail lamps are illuminated when the headlamp switch is placed in either the PARK or HEADLAMP position. The park and tail lamps are grounded at G202.

The marker lamps are illuminated when the headlamp switch is placed in either the PARK or HEADLAMP position and the marker lamp defeat switch is in the ENABLED position. The RIGHT HAND PARK LAMP fuse in the I/P fuse block, supplies battery positive voltage to the coil side of the marker lamp relay. The MARKER LAMP fuse in the I/P fuse block, provides battery positive voltage to the switch side of the marker lamp relay. When the marker lamp defeat switch is placed in the ENABLE position, a path to ground is supplied to the marker lamp relay. This activates the marker lamp relay. The marker lamp relay supplies battery positive voltage to the marker lamps, the trailer tow connector, and the body builder connector. The marker lamps are grounded at G101 and G102.

The TURN BACKUP LAMPS fuse in the I/P fuse block, supplies ignition positive voltage to the turn signal switch. The turn signal switch supplies ignition positive voltage to the turn/hazard flasher module. With the turn signal switch placed in either the left or right turn position, the turn/hazard flasher module sends an on-off voltage signal to either the left or right turn signals and their instrument panel cluster (IPC) indicator. The turn/hazard flasher module is grounded at G101. The HAZARD fuse in the I/P fuse block supplies battery positive voltage to the hazard switch. The hazard switch supplies battery positive voltage to the turn/hazard flasher module. When the hazard switch is placed in the ON position, the turn/hazard flasher module sends an on-off voltage signal to all turn signal lamps and their IPC indicators. During turn signal and hazard lamps operation, the on-off voltage is also supplied to the trailer tow connector. The turn signal lamps are grounded at G202.

The CHMSL fuse in the I/P fuse block, supplies battery positive voltage to the switch side of the center high mount stop lamps (CHMSL) relay. The STOP fuse in the I/P fuse block supplies battery positive voltage to the brake switch. When the brake switch is activated, the brake switch supplies battery positive voltage to the BRAKE ISO fuse in the underhood fuse block assembly. The BRAKE ISO fuse supplies battery positive voltage to the body builder connector and to the coil side of the CHMSL relay. This activates the CHMSL relay. The coil side of the CHMSL relay is grounded at G103. The CHMSL relay supplies battery positive voltage to the turn/hazard switch. The turn/hazard switch supplies voltage to the stop lamps. The stop lamps are grounded at G202.

The BRAKE fuse in the underhood fuse block assembly, supplies battery positive voltage to the switch side of the brake lamp relay. The STOP fuse in the I/P fuse block supplies battery positive voltage to the brake switch. When the brake switch is activated, the brake switch supplies battery positive voltage to the BRAKE ISO fuse in the underhood fuse block assembly. The BRAKE ISO fuse supplies battery positive voltage to the coil side of the brake lamp relay. The coil side of the brake lamp relay is grounded at G103. This activates the brake lamp relay. The brake lamp relay supplies battery positive voltage to the trailer tow connector.

On vehicles with RPO M74, MX4, and MTW, the Turn Backup Lamps fuse in the I/P fuse block, supplies ignition voltage to the switch side of the reverse lamp relay. The ENGINE 3 fuse in the underhood fuse block supplies battery positive voltage to the coil side of the reverse lamp relay. When the transmission control module (TCM) receives an input that the transmission is in reverse, it provides a path to ground for the coil side of the reverse lamp relay. This activates the reverse lamp relay. The reverse lamp relay then supplies ignition voltage to the backup lamps. The backup lamps are grounded at G202.

For all other transmissions, the Turn Backup Lamps fuse in the I/P fuse block supplies ignition voltage to the backup lamp switch or the neutral start backup switch. When the transmission is placed in reverse, the appropriate switch supplies ignition voltage to the backup lamps. The backup lamps are grounded at G202.