reverse light on dash for a-833

I have a 1970 dart swinger with a the a-833 and the reverse light on the dash is not working. There is nothing plugged into the tranny, and I have no idea where to start. I found a wiring set and online for it but don't know where it all goes. Does the wiring from the tranny plug into the block on the firewall? Where does the single wire from the light on the dash connect to? Any advice would help.