Weird tail light problem

Having a strange problem with left rear tail light. With running lights on all is normal. If I use the left blinker with lights on it blinks a little bit faster and running lights dim some as it blinks and backup lights will glow dimly and go off with the blinker. If I push the brake pedal it blinks faster and everything dims and gets brighter with the blink. No lights or brake blinker works normal until I push brake then a little faster blink and it all dims and gets brighter with blinker.
Changed bulbs and checked wiring and plug still no change. Anyone have any ideas what's going on?
Thanks

 

Factory lights? Or aftermarket? Is this truck new to you, or has it been working fine for a while?

 

It's the original factory tail light. Never any problems bought truck new.
I just ordered a new tail light assembly. Figured since the other side works fine it must be either the sockets or plug. Will have the new one in a few days and see if that fixes the problem

 

Could be bad ground (located beside clutch pedal behind kick panel) bad connections at taillight, corrosion, loose crimp.

I would check for voltage at taillight connector and see what you are getting. Make sure both grounds (2 of the 6wires) are good.

 

Must be something at the tail light because the other side works fine. Will check the ground at the sockets. Thanks

 

Solved problem. It's a problem with the ground to that tail light. Ran a separate ground and works perfect. Cancelled tail light order.