Rear brake and rear turn signals not working

Check wiring harness may be broken somewhere or check relays and fuses.

Has the vehicle been in an accident on the left rear side. First check the bulb to be sure it is not defective, trade it out with the side that works properly to test. If the bulb works well then My thought are you may have a shorted wire. The turn signal flasher works by heat build up within the flasher the heat is caused by the load of the bulbs, the load heats the metal spring causing it to open the circuit then as quickly as it cools down the circuit closes again lighting the bulbs.
There is also a possibility of a defect in the turn signal mechanism on the steering column. The turn signal switch on many models does three different things on many models that use the same bulb element / or bulb for brake and turn on rear of vehicle. It controls the circuit for brake light by sending power both left and right side rear when turn signal is in neutral position then when turn signal is in left turn the switch cancels brake light power to left side rear and supplies flasher power to left side while maintaining brake light supply to the right side rear, and so on opposite when the right turn is chosen on turn signal switch. The turn signal indicators on the dash normally run off the same circuit as front turn signal bulb only which is also controlled by turn signal switch. Front has turn signals but no brake light.
I think there is an additional load on the left side rear turn circuit and it could be either a wire that is shorted or the turn signal switch if the same bulb element is used for both functions.
Often times if trailer lighting is connected the flasher will also blink a little faster because of the extra load of additional bulbs.

If you have no power getting to the circuit, it could be the turn signal switch. The brake circuit goes thru the turn signal.

feed supply problem somewhere ?but where ? try checking the wiring loom at the rear or as its called in american "pigs tails"

The bulb for the turn signal/brake light is a double filament bulb. It will come on with the lights on, but should light the second filament, making it brighter, with the brakes applied or turn signal on. It could just be a bad bulb, but one common problem on these years of truck is the rear light circuit board and requires the whole assembly to be replaced. Start by checking the bulb first though.
Hope this helps. Good luck!

Normally with the blinker blinking really fast, it's telling you that one of the bulb is blown, front or rear signals. Check your fuse, and fuse relay to see if it would fix the promblem

check the rear lower bulbs, if good nore than likely brake lamp switrch on brake pedal, 3rd lamp rns of separate circuit

Replace the turn signal switch. Bad contact inside causing a crossing of the circuits. When the turn signal is applied it should open the brake light circuit allowing for just the signal to work. Doesn't sound like the switch is doing it's job.

I had this problem, and to be honest, it happened to the left side about a week later...it's the board that the bulbs plug into...it's a very common problem with this model. So popular that you can normally get the socket board off the shelf at a parts store! it's extremely simple to replace, and I replaced all the bulbs at the same time!

If you're talking about rear brake lights not working there is a recall for the circuit boards behind the bulbs that overheat. THe board will blow the light bulbs as fast as you can replace them.