Get a test light. Put a fuse in.
With KOEO, put the trans into reverse. Test the power into the reverse switch, C111, BLK w/ Yel. Test power out of reverse switch, C111, BRW, w/WHT.
If no power out of the switch, then replace switch.
If both of these are good, move to the rear.
Test wire at rear harness C159, BRW w/ WHT. If power getting to the rear, then test the sockets.
If any of these do not light the test light search for breaks before the fail point. Between C111 and C159, there are several connectors (C104, 157, 158) that all have BRW w/ WHT wires. Wire breaks or corrosion could disrupt the power.