Ive Got a 1999 Chevy Express 1500. When driving my taillights are bright but when braking the lights dim. It looks exactly like the opposite as it should be. I need to get this fixed because its an obvious safety issue. Any help appreciated!
I would start with making sure the brake light circuitry is well grounded.
Next I would start looking for loose frayed wires.
After that start checking circuits with a voltage meter.
After that……. I would be scratching my head lost. jonny
Dual filament light bulbs sometimes break the top filament and the end falls down on the lower filament of the light bulb causing the the light to dim when you push the brake petal as the broken brake light filament is now using the running light filament in the bulb as a ground. I would start by replacing both/all rear dual filament bulbs.