The exterior lighting system consist of the following lamps:

Two circuit breakers in the Instrument Panel (IP) fuse block supply battery positive voltage to both the left and right headlamp assemblies. The low beam headlamps are both connected to ground through the lighting relay and the lighting high/low relay. The high beam headlamps are connected to ground through the lighting high/low relay. A circuit breaker in the Instrument Panel (IP) fuse block supplies battery positive voltage to the lighting relay coil circuit for headlight control. When the driver places the headlamp switch in the HEADLAMP position, the lighting relay is energized. Depending on the position of the dimmer switch, the high/low relay is either energized for high beam operation or off for low beam operation. For low beam operation, the coil circuit of the lighting relay is connected to the low beam circuit of the dimmer switch. The low beam circuit is then connected through the headlamp switch, to ground at G105. For high beam operation, the coil circuit of the lighting relay is connected through the diode module, to the high beam circuit of the dimmer switch. The coil circuit of both the lighting relay and the high/low relay are then connected through the headlamp switch, to ground at G105. A circuit breaker in the Instrument Panel (IP) fuse block supplies battery positive voltage to the high beam indicator. The high beam indicator is connected to ground G105 through the same high beam circuit of the dimmer switch. When the headlamp dimmer switch handle is pulled toward the driver, the flash-to-pass switch closes, grounding the high beam circuit at G105. With the headlights in the low beam position, the high beams may be momentarily turned on or flashed with the dimmer switch handle.

If the headlight switch is left in the ON position, the headlights will remain on until turned off or the battery runs dead.

The daytime running lamps (DRL) will illuminate the low beam headlights at a reduced intensity. A circuit breaker in the Instrument Panel (IP) fuse block supplies ignition positive voltage to three separate DRL relay coil circuits. The low beam headlamp circuit is connected to the DRL resistor through the normally closed lighting relay. The DRL resistor is used to reduce the low beam intensity during DRL operation. The DRL circuit continues through the normally closed DRL ON relay switch contacts, and the energized DRL OFF relay switch contacts to G105. The coil circuit of the DRL ON relay is controlled by the generator, if the engine is stopped the relay is energized and the DRL is off. The coil circuit of the DRL OFF relay is controlled in two different ways. If the vehicle is equipped with hydraulic brakes, the circuit continues through the normally closed switch contacts of the DRL OFF #2 relay to G105. A circuit breaker in the Instrument Panel (IP) fuse block supplies ignition positive voltage to the coil circuit of the DRL OFF #2 relay. The coil circuit of the DRL OFF #2 relay is controlled by the park brake switch and is grounded at G105. If the vehicle is equipped with air brakes, the coil circuit of the DRL OFF relay is controlled by the park brake switch and is grounded at G105. The DRL will operate any time the engine is on, the headlight switch is in the OFF position and the park brake switch is closed. When these conditions have been met, the DRL will illuminate.

The park, tail and marker lamps, including the license lamps, are turned on when the headlamp switch is placed in the PARK or ON position. A circuit breaker in the Instrument Panel (IP) fuse block, supplies battery positive voltage to both the tail lamp relay switch contacts and coil circuit. The circuit breaker in the Instrument Panel (IP) fuse block also supplies battery positive voltage to the marker lamp relay switch contacts and the marker lamp switch. The tail lamp relay coil circuit is controlled by the headlamp switch. When the tail lamp relay is energized voltage is applied to the tail lamps, mirror lamps and side marker lamps. The tail lamp relay also applies voltage to the interior dimming circuit, trailer lights and the interior upfitter connector. The marker lamp relay coil circuit is controlled with the marker lamp switch. When the driver places the marker lamp switch in the ON position, current flows through the marker lamp coil circuit to ground G105. The marker lamp relay applies voltage to roof clearance lamps and the trailer connector. When the driver places the marker lamp switch in the ON position, a LED in the switch illuminates. The marker lamp switch LED is grounded at G105.

A circuit breaker in the Instrument Panel (IP) fuse block, supplies battery positive voltage to the turn signal/hazard flasher module. Circuit breakers in the Instrument Panel (IP) fuse block, also supply battery positive voltage to both the left and right turn signal trailer relays and the stop lamp switches. The turn signal/hazard switch grounds either the left or right turn input circuits of the turn signal/hazard flasher module at G105. The turn signal/hazard switch grounds both left and right turn inputs at G105, for hazard flasher operation. When the turn signal switch is placed in either the left or right position, the circuit is complete from the flasher module to the turn signal/hazard switch and to ground G105. The flasher module then sends an on-off voltage signal to either the left or right turn signals and their instrument panel cluster (IPC) indicator. The flasher module also sends an on-off voltage signal to either the left or right turn signal trailer relay for trailer lamp operation. When the hazard switch is pressed, all turn signal lamps will flash including both IPC turn indicators. The front turn signals are grounded at G107. The rear turn signals are grounded at G405.

If the vehicle is equipped with hydraulic brakes, there is one stop lamp switch. If the vehicle is equipped with air brakes, there are 2 stop lamp switches. A circuit breaker in the Instrument Panel (IP) fuse block, supplies battery positive voltage to the normally open stop lamp switch. When the driver presses the brake pedal, the switch contacts close and battery positive voltage is supplied to the turn signal/hazard flasher module for stop lamp operation. Battery positive voltage is also supplied to the multifunction alarm module and the inverter driver module if equipped. Battery positive voltage is also supplied to the powertrain control module (PCM) if equipped with a CAT powertrain. Battery positive voltage is also supplied to the trailer stop lamp relay coil circuit for trailer lamp operation. The current flow is now to the stop lamps which are grounded at G405.

If the vehicle is equipped with a manual transmission, a circuit breaker in the Instrument Panel (IP) fuse block, supplies ignition positive voltage to the normally open backup lamp switch. If the vehicle is equipped with an automatic transmission, the transmission control module (TCM) and the vehicle interface module (VIM), supply the voltage to the backup lamps. When driver places the gear selector lever in the REVERSE position, either the backup lamp switch closes, or the VIM sends ignition positive voltage to the backup lamps. The backup lamps are grounded at G405.