Any time the battery is hooked up, the breakaway switch has current going to it in order to activate the brakes if the pin is pulled from the switch body and there isn't a fuse since that would be a "weak point" in that safety system (it wouldn't do any good to have the break away switch activated in an emergency only to find the fuse was bad, broken or corroded). It is common for the bar brackets for the WDH to be installed too close or right on top of the switch's wires (sloppy installation, but, far too common). After the dealer installed my Equal-i-zer, I relocated the switch a safe distance from the brackets and made sure there was enough slack in the wires to prevent them abrading themselves bare.
Repairing the wires should make the system right as rain; the switch itself should still be OK. You didn't do anything wrong.
My 2 cents, your mileage may vary...
2 Cats; J-Lo and Ragamuffin :R
2014 Thor Tuscany 40RX DP
2011 Ram 2500 Longhorn CTD HO
2011 Keystone Cougar 318SAB (now gone)
2008 FunFinder X 210WBS (Sadly gone)