Hi,The rear indicators are supposed to work in the tails on this model.
Fuses should not be an issue as they run the same for both sets of lamps.
I would want to go the harness for the tow bar and unplug it and see if normal operation is restored; the more common harnesses that use a built in modulator are very common to malfunction even when brand new, and as well it is possible that things were damaged during install depending on kit type. If it is the scotch-lock type connectors we regularly see these actually sever the wires they are tapped to rather than just puncturing them, resulting in the current no longer reaching the original destination. If they used this sort of kit that would certainly explain the loss of signals on the tails.
In either scenario, returning the wiring temporarily to stock will likely show if that is the case (either via the modulator malfunctioning causing the lights to stop, or if the wires are damaged you'll see during disconnection).