I had a phantom electrical problem on a car once that turned out to be a cracked wire rubbing on a metal edge under the dash... it would simply ground out at times, causing a surprising range of electrical issues including radio failure, doorlock failure, starter motor failure... it took two years to find, as every time I would take it to a dealer or an electrical shop, they would find nothing wrong.
The good thing in your case, with RE electrics is they are so simple in comparison.
Check your wiring wherever it might rub... up in the headlamp casque on the front fork seems a likely candidate; but also where the wires enter the rear mudguard, or go into the toolbox, or exiting the primary from the alternator.