TheAmRheins wrote:
The brake wire that runs through the axle tubes is possibly frayed inside the axles.
The key is it is INTERMITTENT. Grounds, factory brake controller, and plug connections usually are not intermittent. Although sometimes they can be. But not usually.
Quote above a strong possibility. As well as, a wire inside the wheel hub has just started to rub through. And when the brake levers engage they move against the wire. Sometimes it shorts out. Sometime it may not. Eventually the problem will get worse, as the worn insulation area gets larger.
Best to remove the wheels (one at a time) and check the wires in the hub very closely. Especially where they run close to any movable metal levers. This can be quite costly for labor. But not for parts. The fix can be as simple as installing a piece of shrink wrap insulation. And re-routing the wire so it does not rub anything.