I just repaired a rear wiring loom for a bloke who has a Fatboy of similar vintage. It had intermittent rear brake, tail, indicator & dash issues over several months which got progressively worse. It might be worth jacking the bike up and having a good look up under the rear guard. The wiring loom is double sided taped to the guard. In his case the tape had let go towards the front of the guard allowing the wiring to drop slightly and touch the back tyre when the suspension was compressed, slowly wearing away the insulation on the wiring, severing two wires & shorting out a few more. The symptoms were similar to yours at the start but got worse as time went on.
Enjoy the ride.
Thanks to all for the welcome and the advice on the electrical issues. I have tried all options thrown out there by some members but unfortunately I still have the fault. I have spoken to the local dealer again but they cannot promise me it wont be an expensive find/fix.
All your advice has been greatly appreciated. Might just keep riding and just live with it