I would check to see if the jack is getting power. To do this I would slightly cut into the positive power wire going to the jack and with a volt meter check to see if you have 12 volts from the power wire to ground. If you have power than its the switch or the jack. If no power than check the wire back to the battery or fuse block. Thats what I would do.
2012 Jayco Eagle 321RLTS
2008 Dodge Cummins 3500 DW Crew Cab 4x4 6 speed Auto, Exhaust Brake