Daytime Running Lamp: Description and Operation

The headlamp system for Canada vehicles contains a daytime light control unit that activates the high beam headlamps at approximately half illumination whenever the engine is running. If the parking brake is applied before the engine is started the daytime lights will not be illuminated. The daytime lights will illuminate once the parking brake is released. Thereafter, the daytime lights will continue to operate when the parking brake is applied.
Power is supplied at all times
^ through 15 A fuse (No. (53), located in the fuse and fusible link box)
^ to headlamp relay LH terminals (1) and (3)
^ through 15 A fuse (No. (54), located in the fuse and fusible link box)
^ to headlamp relay RH terminals (1) and (3).
^ through 15 A fuse (No. (66), located in the fuse and fusible link box)
^ to tail lamp relay terminals (1) and (3).
With the ignition switch in the ON or START position, power is supplied
^ through 7.5 A fuse [No. (12) ,located in the fuse block (J/B)]
^ to daytime light control unit terminal (3), and
With the ignition switch in the START position, power is supplied
^ through 7.5 A fuse [No. (33), located in the fuse block (J/B)]
^ to daytime light control unit terminal (2).
Ground is supplied to daytime light control unit terminal (16) through body grounds (E5) and (E30).

DAYTIME LIGHT OPERATION
With the engine running, the lighting switch in the OFF or 1ST position and parking brake released, power is
supplied
^ through daytime light control unit terminal (7)
^ to terminal (3) of RH headlamp
^ through terminal (1) of RH headlamp
^ to daytime light control unit terminal (9)
^ through daytime light control unit terminal (6)
^ to terminal (3) of LH headlamp.
Ground is supplied to terminal (1) of LH headlamp.
^ through daytime light control unit terminals (10) and (16)
^ through body grounds (E5) and (E30).
Because the high beam headlamps are now wired in series, they operate at half illumination.