Motor off and in Park lights on everything works when I turn the left blinker on everything works fine I'll turn the right blinker on the left rear tail light goes out same thing when I hit the brakes the left rear tail light goes out.

 

Also I have the fast blink on both back lights if it has anything to do with it

 

Pleaase list our vehicle details

 

Sorry 2003 Chevy Express 2500

 

I suspect you have a bad ground on the left taillight/brake light. When you're not braking or signaling, current from the left taillight makes its way to ground via a sneak path through the left brake/turn filament and then over to the brake/turn filament on the other side and then to ground. Applying brakes or using the right turn signal blocks this sneak path and the left taillight goes out.

 

Cool thank you
I will let u know