Need some wiring help....

[Z28Owner]

On my 71 truck, I replaced both brake lights and flasher box. I cant figure out why one works and other doesnt. My drivers side turn signals, brake lights and parking lights all work. My parking lights work on Pass side, but no turn signal or brake light. I swapped bulbs and still same thing, so Its not a bad bulb. I have checked all the wiring around the bed its all fine. Could someone fill me in on how or what this could be if you have had the same problems, TIA - Jason