2001 Bluebird conventional with Allison 2000 series has no reverse lights. Where does this signal come from? Is it integrated into the NSBU switch? Does it go to a relay somewhere on the bus?
Update: After some checking around and getting angry, I took a lens off and found power at the light, but the housing had a bad ground. Checked the other side, and the ground strap was broke off. These are the older style lights that use the plastic housing with the ground strap screwed to the plastic in the middle of the housing. Replaced entire assemblies, all is good now.