I have a 94 Chevy C1500 and the right side brake light and blinker are not working. The tail light and reverse light work though, and the right front blinker works but it blinks twice as fast as it should. All of the left side brake and blinkers work fine. I replaced the bulb, tail light circuit board, and tried a flasher from another Chevy truck that I know was working and still there was no change. What could it be?

It could be a bad multifunction (turn signal) switch. The way that switch works, it is possible that it can turn on the front blinker and not the rear one. It also cancels the brake circuit so the turn signal can work with the brake pedal depressed.

However, a more likely cause would be a break in the YELLOW/BROWN wire at the rear of the truck. It is common for the connector to get corroded at the left rear frame area where the bed harness connects to the vehicle harness. If you have trailer connections spliced into the wiring harness, these connections are also prime candidates for corrosion. I would look there first. Inspect these harnesses thoroughly all the way up and into the tail light assembly.

If the wires under the back of the truck look good, then I would check for power coming out of the turn signal switch. The wire at the turn signal switch is plain YELLOW (with no brown tracer). It is Pin (M) on the turn signal switch connector. The front signal is a LIGHT BLUE wire at the turn signal switch Pin (H). If you probe these with a test lamp, they should both work the same except the yellow wire will be hot with the brake pedal depressed and the switch NOT in the left turn position. If there is no power at the switch connector, replace the switch.

Well its blinking fast to tell you the rear lamp is out. if you already tried to replace it with no luck try to first take a small flathead screwdriver and make sure the contacts are not corroded and make sure they are making contact with the bulb and if they are check the line and make sure there are not any broken or loose wires