No reverse light 2011 Peterbilt 337, Allison automatic trans

The wire to the reverse lights goes from the lights into the cab, doesn't stop anywhere along the way. I can apply +12V to that wire at the cab and lights come on. So, no break in the wire. Someone, just going off of documentation, told me they're run by a chassis node mounted on the chassis, which is run by a CECU. But I see no chassis node anywhere under the truck. I checked another Pete 337 and that one doesn't appear to have this chassis node neither. Supposedly, this is how 2010+ is supposed to work (CECU + chassis node). Anyway, the wire goes into a large harness behind the steering column and gets lost from there.

Does anyone have a wiring diagram they can share? If I could just find out where that wire originates, wehre that item is located... Relay? TCM? Chassis node?