WHY do you have to pull pin to wrap cable around bumper?
Cable should have loop on end......get a carabiner or 'S' hook with spring clip and attach cable to safety chains.
Emergency Break Away Switch shouldn't activate unless trailer is completely disconnected from tow vehicle........ trailer jumped ball, safety chains broke, umbilical cord pulled out...trailer run-away
When you pull pin.......full battery voltage is going to trailer brake magnets
and IF truck/trailer umbilical cord is plugged in.......you can backfeed to brake controller in truck.
Applying full battery voltage to magnets.......not an issue unless it is done for extended time (hours) and then damage could be done to magnets/wiring etc.
Depending on which brand of brake controller......could burn it out