Were the lights working prior to the Invisibrake installation? How far away is CW that installed the Invisibrake? I would think it's a broken wire or a wire pulled out from the connector.
I do not know of a fuse for one side only. Perhaps there is, but I would believe that is unusual.
If the light were working prior to the Invisibrake installation and are not now working, take the coach back to CW for repair.
FMCA #F431170, GS #822128658, Escapees SKP #112655
2012 Airstream Mercedes Interstate Class B