I have a 1995 Chevy Silverado Z71, I am having problems with my tail lights where when my headlights are on and I hit the breaks the driver side tail light completely turns off, if I use the left blinker it blinks very fast up till I hit the breaks. When my headlights are off they still don’t work properly but legal enough, the left blinker blinks in between fast and slow and when I use the brakes the left side works but very dim, the wiring is all original never tampered with, all I did was put aftermarket tail light covers on it which shouldn’t affect anything. The problem usually comes and goes but this last time it lasted for 2 months and now everything works perfect, the problem will be back and I’m afraid I’ll run out of luck and a cop will finally notice it. Any help would be very appreciated.
Start by cleaning all the tail light receptacles and replacing all the bulbs. I would also replace the turn signal blinker. It’s all maintenance anyway. You have a weak link in your brake system and doing this will probably eliminate it.
The tail light sircuit boards
are a likely cause of your problem
The problem might be with the multi-function switch.
All the exterior lighting circuits pass thru this switch.
These switches can wear where when you operate one circuit in the switch it can have negative effects on other circuits that pass thru the switch.
Clean all the grounds you can find.
I think @insightful is on to the trouble. The ground for that side has a connection problem so there is added resistance to ground. When the higher current for the brake light is needed then there is more voltage drop across the added resistance of the bad connection to ground. That is really noticed in the running light operation which has a higher resistance compared to the brake light. To prove there is bad ground you could run a jumper lead to the tail light ground and to a known good ground point. If the lights then work normally then you have proved the cause of the problem.