There are two switches on the transmission which use the same plug one is for the backup lights and the other is for the 5th gear EGR swich if you put the trans into 5th gear and the backup lights come on the wires are switched. Dave
If you have a later model trakick, then the tranny will only have the reverse switch.....they did away with the 5th gear switch, sometime in the early 90s (92 or 93, I think).
All samurai trannys have both switches.
The reverse switch simply passes 12V through it, when the tranny is shifted into reverse.....so you could probe the wires to see if you are getting 12V into and out of the switch.