1969 C10 Turn signals don't work and one brake light doesn't work

I'll try to make this short. My left brake light does not work and when I got the truck none of the lights worked at all. We went through and used a trailer light harness to replace the wires going to the tail lights, same with the turn signal housings. Countless hours we've spent trying to figure this out and the one thing I haven't done is replace the housings for both the tail lights and turn signals, would the ground in the housings be enough to cause them not to work? When I use the turn signal switch the lights when the lights are on they don't even blink, the front turn signal and rear tail light get brighter only unless the headlights are off, then they will actually blink like normal. I know the ground for these lights goes off of the socket so that's what's making me think it's the housings. Am I wrong? I'm thought about getting a different turn signal switch, but am unsure of that too since the wires look ok