3 wire switch pins are (center pin) = neutral safety
two outer pins are for backup lights 12v volts into it and the other to the backup lights.
Lights are grounded to body close to where they are located.
Well at least the timing is good, I'm about finished with the drive-train and starting to sort out the lights. And sure enough the backup lights don't work. So far it's been pretty easy as most are just ground issues and the harness has never been hacked up.