Rear light problem

[NO LIFT]

'88 Carrera

Lights off, brake pedal depressed:
-Right brake light normal
-left running light comes on as brake light

Lights on:
-two normal running lights

Lights on, brake pedal depressed
-Right light bright
-Left running light goes out, no brake light.

What gives?

[Arne2]

Bad ground on the left light.

[timmy2]

I'm sure you have replaced the bulb and tested the replacement in the normal working socket on the right.
1. Possible bad ground left side housing.
2. Socket is failing in the housing.
Numerous posts about the sockets failing at the back.

[NO LIFT]

Thanks to both-

Bulb is good, I'm suspecting I have both issues listed by Timmy2, I've had loose sockets on the turn signals.

Guessing that the ground is behind the housing, I think I remember a couple bolts behind the lens. Anything I should be aware of (I have the terrible habit of breaking things that I haven't taken apart before)?