John Clark,
I don't know how the truck was wired from the factory. If you want brake light and turn signals on the back you will need either a double filament lamp on each side, OR, two single filament lamps on each side.
Without special gizmo's, each function...brake, and tail need their own dedicated filament. So this can be one lamp with two filaments, OR two lamps with one filament each. If you aren't totally confused yet, I can try again.
Stuart
