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That wire should go to the trailer frame. My wiring goes into a junction box on the front of the frame, and continues to the frame from there. It doesn't go directly to the battery.
Every day's a learning experience, though sometimes not what we expected.
2012 Jay Flight 19RD
2016 Ford F150 XLT 2X4 SC 3.5L Eco Max Tow
2010 Tundra TRD DBL Cab (Traded)
2 new fluffy Corgis, Bayley and Stanley