This tip is from an Excel 5th Wheel Owner ... "I have a turn signal auto flasher velcroed on the inside of my pinbox (keep it out of the weather), just in case I have an emergency situation, where I have to leave my unit on the roadside at night (or dark day) without the tow vehicle attached. Simply plug the flasher into the trailer plug at the no.3 (green wire - taillights) and no.4 (black wire - B+)
This will use the trailer batteries to flash all running and taillights to warn motorists. You may have to bend the flasher terminals just a little to accommodate the angle of the female terminals. Flasher is cheap at about $3.-4. at local auto parts or Walmart."