For 1990-2009 cars

### Exterior Lamps

The exterior lighting system consist of the following lamps:

• | The headlamps

• | The daytime running lamps (DRL)

• | The park, tail, and marker lamps

• | The turn signal lamps

• | The stop lamps

• | The backup lamps

### Headlamps

The HEADLAMP fuse in the underhood fuse block 2 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 HIGH BEAM position, battery positive voltage is supplied directly to the high beam headlamps. With the headlamp dimmer switch in the LOW BEAM position, the headlamps dimmer switch supplies battery positive voltage to the switch side of the daytime running lamps (DRL) relay, and to the low beam headlamps. Both headlamps are grounded at G101 or G111.

### Daytime Running Lamps (DRL)

The daytime running lamps will illuminate the low beam headlamps at a reduced intensity. The daytime running lamps (DRL) will operate when the ignition is ON, the headlamp switch is OFF, and the park brake is disengaged. The HEADLAMP fuse in the underhood fuse block 2 supplies battery positive voltage to the headlamp switch. The headlamp switch then supplies battery positive voltage to the DRL relay, through the DRL diode. The DRL diode drops the amount of voltage going to the DRL relay. Ignition voltage is supplied to the coil side of the DRL relay by the IGN SW circuit breaker in the instrument panel (IP) fuse block. The DRL control module supplies ground to the switch side of the DRL relay. This activates the DRL relay and supplies voltage to the low beam headlamps. Both headlamps are grounded at G101 or G111.

### Park, Tail and Marker Lamps

The park, tail, and marker lamps are illuminated when the headlamp switch is placed in either the PARK or HEADLAMP position. The PARK LP circuit breaker in the instrument panel (IP) fuse block supplies battery positive voltage to the switch side of the lighting relay. The coil side of the lighting relay is grounded at G101 or G111. When the headlamp switch is placed in the PARK or HEADLAMP position, battery positive voltage is supplied to the coil side of the lighting relay. This activates the lighting relay. The lighting relay then supplies battery positive voltage to splice 209. Splice 209 distributes the battery positive voltage to the park lamps, tail lamps, clearance and identification lamps, and lighted mirror lamps, if equipped. Splice 209 also supplies battery positive voltage to the upfitter connector and the tractor trailer receptacle, if equipped. The park lamps, clearance and identification lamps, and the left side lighted mirror lamp are grounded at G101 or G111. The right side lighted mirror lamp is grounded at G210. The tail lamps are grounded at G405.

If the vehicle is a Super Chassis w/JE4 and RQ3/U86, it will also have a tractor marker lamps relay. The MRK LP circuit breaker in the IP fuse block supplies battery positive voltage to the switch side of the tractor marker lamps relay and the trailer marker lamps switch. The coil side of the tractor marker lamps relay is grounded at G101 or G111. When the trailer marker lamps switch is placed in the ON position, battery positive voltage is supplied to the coil side of the tractor marker lamps relay. This activates the tractor marker lamps relay. The tractor marker lamps relay then supplies battery positive voltage to splice 205. Splice 205 distributes the battery positive voltage to the clearance and identification lamps, upfitter connector, and tractor trailer receptacle. The clearance and identification lamps are grounded at G101 or G111.

### Turn Signal Lamps

The TRN HAZ circuit breaker in the instrument panel (IP) fuse block supplies battery positive voltage to the hazard lamps flasher. The hazard lamps flasher is grounded at G101 or G111. The hazard lamps flasher supplies battery positive voltage to the turn signal switch and the hazard warning switch, if equipped. When the turn signal switch is placed in either the left or right turn position, the circuit is complete from the hazard lamps flasher to the turn signal lamps and to ground. The hazard lamps flasher then sends an on-off voltage signal to either the left or right turn signals and their instrument panel cluster (IPC) indicator. When the hazard switch or hazard warning switch is placed in the ON position, the circuit is complete from the hazard lamps flasher to all turn signal lamps and to ground. The hazard lamps flasher sends an on-off voltage signal to all the turn signals and their IPC indicators. During turn signal and hazard lamps operation, on-off voltage is also supplied to the tractor trailer receptacle. The front turn signal lamps are grounded at G101 or G111. The rear stop and turn signal lamps are grounded at G405.

### Stop Lamps

The STOP circuit breaker in the instrument panel (IP) fuse block supplies battery positive voltage to the stop lamp switch and the switch side of the stop lamps relay. The coil side of the stop lamps relay is grounded at G111. When the brake pedal is pressed, the stop lamp switch supplies battery positive voltage to the coil side of the stop lamps relay. This activates the stop lamps relay. The stop lamps relay then supplies battery positive voltage to the turn signal switch. The turn signal switch then supplies battery positive voltage to the stop and turn signal lamps. The stop and turn signal lamps are grounded at G405.

If the vehicle is a Super Chassis w/JE4 and RQ3/U86, there will also be a trailer stop lamps circuit. The STOP circuit breaker in the IP fuse block supplies battery positive voltage to the stop lamp switch and the trailer stop lamp switch. The TRANS TRLR fuse in the underhood fuse block 1 supplies battery positive voltage to the switch side of the trailer stop relay. The coil side of the trailer stop relay is grounded at G111. When the stop lamp switch or trailer stop lamp switch is activated, battery positive voltage is supplied to the coil side of the trailer stop relay. This activates the trailer stop relay, and it supplies battery positive voltage to the tractor trailer receptacle.

### Backup Lamps

On vehicles with RPO MWF, the BU AND IGN 3 circuit breaker in the instrument panel (IP) fuse block supplies ignition voltage to the switch side of the reverse warning relay. The IGN SW circuit breaker in the IP Fuse Block supplies ignition voltage to the coil side of the reverse warning 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 warning relay. This activates the reverse warning relay. The reverse warning relay then supplies ignition voltage to the backup lamps. The backup lamps are grounded at G405.

For all other transmissions, the BU AND IGN 3 circuit breaker in the IP fuse block supplies ignition voltage to the backup lamp switch or the park/neutral position and backup lamp switch. When the transmission is placed in reverse, the appropriate switch supplies ignition voltage to the backup lamps. The backup lamps are grounded at G405.