Left brake light wont come on

[TGP Z-34 STE]

I am working on 1990 Grand Prix STE.

 

The problem is. Brake light on driver side, wont come on while top/middle n passenger side light will come on when I hit brake pedal. So far what I did check is. I removed rear brake harness with sockets out of my STE and put in other STE, all of brake (both sides) will works! Then I bought new signal switch, I thought this will be solve this problem, advice by my friend and dealer. Good enu one or member from this forum is right. It will not solve, cuz it didnt.

 

The wires go to brake socket (Driver Side), have 3 wires. Black = Ground. Dark Blue wire for parking light. Light Blue with black strip for brake light. I was looking for bad ground. But there is 1 ground wire go in Socket. If I am correct on this, one ground wire is feeding for both parking light n brake light? If Parking light is working, that mean ground is ok, it is something else is cause this? Isnt there some kind of relay or fuse that is cause this? I cant think of what else to check, HELP PLEASE!

 

In case u wants to know for Passneger side wires color to socket.

Black = Ground

White= Parking light

Dark Blue with white strip = Brake light.

 

Anything question(s)... please ask me!