Dave,

You are referring to the exact scale BLS EWIV coaches if I remember my Roco numbers. Those coaches can be lit in AC or DC using the Roco 40320 Universal Lighting Kit. The axle contacts are included with the lighting kit and are mounted on the underside of the bogie. The AC slider mentioned by Roco is the shorter of the Flusterschleifer. You will also need that little plastic piece which used to be a standard accessory with most Roco coaches. It replaces the plastic piece onto which the slider is mounted and enables you to attach it to the pins on the underside of the bogie rather than by screw. I ended up using the larger Flusterschleifer because I had trouble transferring the smaller one to the adapter piece.
You could also likely even use a LED lighting kit like Maerklin's 74301 (2) and mount the lighting strip on the underside of the roof. You would then have to connect the lighting strip to the Roco wires or use Roco or Viessmann's current conducting couplers (wired). The other possibility would be using Rapido Trains Eazy Peezy Battery powered lighting kit.

Regards

Mike C