If you're wiring is the same as my 21QB the tongue jack and the tow vehicle charge line are both wired to the 30 amp fuse. That's why the jack works when plugged into the tow vehicle. The down side of this when the fuse blows the trailer battery does not get any charge from the tow vehicle. I removed the jack wire from the fuse and went straight to the battery. I don't know about your jack but my jack has a built in 20 circuit breaker. If you don't have the breaker, place one inline on the wire to the battery. Jayco saved the price of a ring connector and some wire with their goofy design.
2018 Jayco Jay Flight 21QB
2012 F150 Ecoboost Crewcab
Amateur Radio K3EXU
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