Gentlemen:

As far as Loco electrical contact problems, as a DCC decoder installer running my own business, I've encountered this on many engines! Mostly Bachmann Steam (4-8-2's, K4-4-6-2's), Athearn-Genesis Diesels, and even some of the older Atlas-Kato, and Stewart diesels(both made by Kato, or Bowser)!

The for the Bachmann  4-8-2 Steam, is to remove the wipers, that curve down toward the rail, and ad spring loaded "pin" wipers on the bottom axle cover, that line up 90 degrees directly with the backs of the wheel flanges!