My 12 volt
line from the tow vehicle comes in through the 7 way cord, into a 25 amp fuse and out of the fuse to a three way connection of the trailer 12 volt
line, the fused VT line and the break away switch hot line. My jack is fed off that hot side of the break away circuit. The trailer 12 volt line is fused at the converter fuse panel. The other leg of the break away switch is wired directly to the brake hot wire, in addition to the TV brake wire from the 7 way plug.
My jack gets it's power from a possibility of three sources. One; from the 12 volt feed from the tow vehicle, two; from the trailer battery, or, three; from the converter. Right now I don't have a battery in the trailer but it's plugged into shore power and all the 12 volt works.