Roger,
If your truck has turn signals, which means on all four corners of the rig, and you have a actuator, or handle in the cab you move to indicate a left or right turn, then you should have a blinker (flasher) located somewhere under or around the dashboard.
These comments only pertain to the REAR lights, as that was your original question.
Power for the brake lights will come through the brake light switch that is actuated by the brake pedal. As Bill pointed out, this switch has only two poles...
Power comes into the brake light switch, upon closure (brake pedal applied) power goes out and heads to the turn signal assembly.
If no turn is indicated, power travels down TWO wires..one to left brake light, one to right brake light.
If a left turn were to be indicated, uninterrupted power would travel to the RIGHT light, through its own wire and illuminate the right BRAKE light...interrupted power (the flasher can) would travel down the other wire, and the left brake light would blink (its now a turn signal!) to signal a left turn.
If your only glitch in the wiring is to get the rear brake lights to work..AND you have turn signals you want to incorporate into the system, your turn signal switch, which usually does have a whole bunch of stuff coming out of it must be connected into the system.
If you don't want or need the turn signal function on the truck..follow Bill's directions!
I would suggest getting a small circuit tester. Most auto parts stores carry a inexpensive one with little bulb inside, a wire with alligator clip and a real sharp probe.
If you can figure out where the power COMES from, and where you want it to go, all you need to do is figure out what goes in the middle, hook it together and pray.
I am simple minded..I try to make my helpful comments simple. If the above "novel" was simple to understand, made sense to you, and might get you on the road to "brake light city" I sure would like to know. If the stuff I spout makes sense only to me, I'll darn well stop spouting.
Stuart
