yeah, mine is that way. no need to cut or splice; there is a second wire from the brake circuit already fished up into the a-frame, and another lead that connects to the charge line that provides +12v. the breakaway switch connects these wires when the pin is pulled, sending unregulated +12v to the brakes.
since the umbilical connects to the brake line as well, if the breakaway switch is actuated, that would send 12v up the umbilical's brake line, back toward the brake controller, which isn't designed to get zapped with the full amperage of the battery from that direction. In a real-life situation, this wouldn't happen, because the pin won't get pulled on the breakaway switch until after the umbilical has already seperated from the tow vehicle. (make sure that the breakaway cable is longer than the umbilical so that it only actuates if the trailer is completely disconnected from the tow vehicle; if its still attached, you want to be in charge of the brakes).
'73 Safari 23'
'00 Dodge Ram 1500 4x4 QC