09 Mack GU Electrical problem help

Hey all, im trying to see if i can get some assistance with a problem regarding a 09 Mack Gu813. Long story short, i have taken over managing a fleet of some heavily neglected and hacked up trucks.

This particular truck is having an issue with the reverse lights staying on. The R always stays lit up on the dash etc. I have gone through all the basic checks, the only thing i have found is when F17 ctrl/sw inputs fuse is pulled out the r on the dash and circuit perform as they should. Kinda stumped here and would love some sort of input.

Another thing to note, is i found the reverse power relay missing for some reason. Even with this relay out the power to the reverse lights and alarm is energized. It really makes little sense.

Thanks everyone.