Dave,
It depends on what you are calling a lamp. You need two filaments, or LED clusters, on each side of the truck, whether there are two single filament bulbs on each side or one dual filament bulb on each side, with the brake/turn lights controlled by the turnsignal switch. It is possible to use a single LED cluster on each side with an extra resistor and diode to the taillight wire, and the brake/turn wire directly attached to the LED cluster.
