2000 GMC C2500 lights

Hi bigsherm. Welcome to the forum. There are two common causes of this problem. Usually a bad ground causes voltage to find an alternate path to ground through the tail lights which is tied to the dash light circuit. In the past this only affected one side. If the right side had the bad ground, the right turn signal would not flash but the bulb would appear to light up. It was hard to notice that it was not as bright as normal. On newer vehicles, the rear turn signal and brake loghts are different bulbs. The left and right brake lights are tied together, so either side can have the bad ground and cause your problem.

Another potential cause, especially on minivans, is a chewed up trailer wiring harness that has wires shorted together. It happens more on minivans because they sit lower to the ground and will scrape when turning into a steep driveway. Also, some older connecotrs from U-Haul had three red leds built in to aid in wiring the system. Those leds commonly short and will in effect connect the brake light circuit to the tail light circuit.

Caradiodoc