If the axles are Dexter, there is a pair of wires that goes through each axle to provide brake power to the other side. Those wires are infamous for getting rubbed on the inside of the axle and shorting out. I'm guessing that the indication of a short to ground is on your electric brake control. I'd have someone activate the manual lever and watching the brake control for a change in the display as you shake and pull slightly those wires, one at a time, that go through the center of each axle. If you isolate the problem to one of those pairs of wires, it is very easy to fix and does not require removing a brake drum to fix.
