Reversed taillight problem

[Youey]

I've been having this problem long before I took my truck apart and it's driving me off the deep and I've tried everything. The problem is my passenger side taillight is reversed. It's dim when you step on brakes and when you turn lights on its super bright like your stepping on the brakes. Little history I've changed harness for taillights and got an fuse box and wiring from another truck that wasn't hacked up like mine was. I have 3 ground straps one on frame to cab, frame to bed, frame to cab again on passenger side. Is there any way that the other harness I installed the wiring is different? It's from a 67-72 chevy. And should I ground the battery from engine block which it is now, I have a pig tail coming off neg side to frame ? Just need some suggestions this is making me nuts.