Can anyone advise me on digitrax decoder installation in a rivarossi Hudson or challenger steam loco. I’ve connected the black lead to the trailing truck rivet for the right rail side pickup. Then I attached the red lead(I think it comes from the frame plate) to the left rail side pickup. the grey and orange leads then connect to the proper motor hookups. The blue light lead runs to the trailing truck rivet and the white light lead runs back to the lamp. I don’t think the motor is properly isolated but I don’t understand how to remove the motor. Can anyone offer advise I haven’t seen any articles on this subject.
I’ve installed decoders in Rivarossi Cab-Forwards, and Big Boys, so if the Challengers and Hudsons are similar, it should be a breeze. To isolate the motor, you just need to remove all the old wires (they were probably black). Where they were attached to, is where you will be soldering the decoder wires. Don’t solder anything to the frame. May I recommend getting one of John Eberle’s bright white LED’s for your headlight. They look like the real thing, and will nearly blind you! 
Call John Eberle’s DCC Headquarters for all your DCC needs. (877)531-5275 He is very nice, has great service, and has installed lots of decoders in Challengers.