Daytime Running Lamp: Description and Operation

OPERATION
When the Headlamp Switch is in the "OFF" position, the Daytime Running Lamps (DRL) see an open circuit at terminal E. This indicates to the DRL Module that the headlamps are off.

If the park brake is not set, the Module sees an open circuit at pin F. When the DRL Module sees these conditions, and when the Ignition Switch in "RUN", the Module applies voltage to the left headlamp HI beam filament. The Module applies voltage to the right headlamp HI beam filament through circuits PR08 (GN) and PR07 (Y). The headlamps then glow at a reduced intensity.

LO Beam Operation
When the Headlamp Switch is put in the "HEAD" position, the DRL Module receives a voltage signal from the Headlamp Switch via circuits LA14 (GY/R) and PR02 (GY/R). The DRL Module removes voltage from the Left Headlamp and applies a ground to circuit PR07 (Y) at the Right Headlamp. The left and right LO beam headlamp filament receives battery voltage through the normally closed contacts of the Left and Right Headlamp Relays. Both LO beam filaments glow a full brilliance.

High Beam Operation
When the high beam switch is pressed and the Headlamp Switch is in the "HEAD" position the Right and Left Headlamp Relays energize. A voltage signal is sent to the DRL Module via circuits LA30 (O/BL) and PR06 (O/BL) when the Right Headlamp relay energizes. The DRL Module applies full battery voltage to the right headlamp Hi beam filament through circuits PR08 (GN) and PR07 (Y). The left HI beam headlamp filament receives battery voltage directly from the Left Headlamp Relay. Both HI beam filaments glow a full brilliance.

Flash To Pass Operation
When the headlamps are in DRL mode and the Flash To Pass Switch is pressed, a voltage signal is sent to the DRL Module via circuits LA30 (O/BL) and PR06 (O/BL). The DRL Module applies full battery voltage to the right headlamp HI beam filament through circuits PR08 (GN) and PR07 (Y). The left Hi beam headlamp filament receives battery voltage directly from the Flash To Pass Switch. Both Hi beam filaments glow a full brilliance.

DRL Disable Feature
When the park brake is set, the Daytime Running Lamps (DRL) Relay is energized voltage is applied to the DRL Module through the DRL diode assembly and circuits PR05 (LG), PR19 (LG), PR05 (LG), PR18 (LG), PR14 (BL/BK) and PR0l (BL/BK). The DRL Module then removes voltage from the circuits supplying voltage to the HI beam headlamp filaments. The DRL System is also disabled if a generator fault is detected. If the generator grounds circuit D8 (Y/BK), this ground signal reaches the DRL Module via the Diode Junction Box to pin A of C133 forcing the DRL Module to save battery power by disengaging the DRL mode.