Voltage is supplied to the fog light relay coil through CKT 74 (LT BLU) when the park lamps are turned on. Voltage is supplied to the load side of the relay at all times through the FOG LP fuse 28. The foglamp coil is grounded through the truck body control module (TBCM) when the foglamp switch is turned on. Voltage is provided to the fog lamps through CKT 34 (PPL) with the fog lamp relay energized.

A voltage signal is also sent from the foglamp relay to the foglamp indicator on the foglamp switch. The voltage signal informs the driver that the foglamps are on.

Ground for the foglamps is provided by CKT 150 (BLK) for the left foglamp to G111. Ground for the foglamps is provided by CKT 250 (BLK) for the right foglamp to G112.

Foglamp relay control is interrupted by the truck body control module when the headlamps high beams are on.