reverse light switch??

my 64 Barracuda reverse lights don't work, the bulbs are good, and when I put it into reverse, the lights flicker once, and stay out. I have the 4 spd with the switch in the side of the case, not on the shifter, as I am used to with some other cars I have owned.

Is there and adjustment on this switch, or is it a good/bad thing only???

Thanks in advance

FF