If the white wire in the umbilical is the source trace that wire back to the male end at the TV connection to determine what it is.
Some older trailer, many brands, used to use romex as the brake feed wiring. The fact that they are using both legs would indicate that is to reduce voltage drop over the length of the wire. Not saying it is the brake wiring but finding the source in the umbilical will tell you.
WBCCI 12156 AIR 3144 WACHUNG TAC NJ6
2004 Excursion 4x4
1991 34 ft. Excella +220,000 miles, new laminated flooring, new upholstery, new 3200 lbs axles