the switch probably has been getting exposed to road spray as most switches are mounted under the skirt. if so ,that may be your problem, the switch could be shorting out.
On my trailer , I put mine in a waterproof switch box with hinged cover.
2013 Sunset Trail 25RB TT
2015 Silverado 2500HD 4x4 6.0 l gasser.
Equilizer 4 pt
From Belle River, Ontario
2003 Mountain Star 890sbrx Truck Camper