rear tail lights wiring help

[cjoenny89]

I am sorry it's a 3 on the tree 1968 c20. I just put my wire harness back on after being off the truck for 25 plus years and recent paint job. Today i ohmed out the wire harness and it was all good. I have to check for power at the other light but I think I didn't get a good connection on the back up light quick connect or I have a bad ground. Reguardless if I slam the shifter in rev. The one back up light turns on then off. Is there an adjustment for it on the 3 speed? I will check the brake light wiring tomorrow.