wouldnt be a wire grounding on the frame, theirs nothing to ground out if their is no power (no brake application) and that would only cause the brakes to fail to operate if it was on the hot side (ground side would have no effect on function)
Check any junction boxes that their is in the trailer wiring, make sure somethings not rattling around in there loose, and in the trailer plug as well (one of the wires could have come loose and is touching the 12v trailer feed or the clearance light post)
As well, like mentioned make sure the shoes are adjusted properly. electromagnet brakes do some funky things and i have also seen "sticky" brakes due to them being out of adjustment.
Last but not least its not uncommon for the brake linings to fall off of the shoes and periodically jam up in the drum. must have done a dozen sets this year where linings have come unglued. If that is the case, dont replace just the shoes, dexter sells the complete backing plate assembly CHEAP, its the only way to go!
'14 XLR 395AMP
'16 Ram 3500 DRW, 6.7 cummins w/aisin trans and 4.10 gears