Both outboard and inboard lights will be both taillight and brake-light.
Reverse lights --> these are grounded at the taillight housing. If they lose ground, they won't work. Jiggle the socket in the housing to see if will ground and light up. Make sure the the socket contacts are clean where it is pushed into taillight housing. Use a test light to see if power is going to the socket.
1967 Chevrolet Impala SS convertible - Ermine White C1
1967 Chevrolet Impala SS 396 - Marina Blue FF