ok its a dumb question but how do you clean the wheels on your locos?
I generally use the Kadee wheel cleaner, which consists of brass brush bristles that are power from the track or power pack. You can find it at most any good LHS.
I like to use the Kadee or Peco wheel cleaner devices as described by ebnut when the wheels are really grimy, but just to add a nice polish, and remove all traces of grease and gunk, you cannot beat a cotton bud (Q-tip) dipped into clean acetone, and applied as the drivers are rotated under power.
Other, non-powered wheels that also collect current can be rotated by finger power and cleaned in a like manner. Acetone sure works for me. :)
On my On30 engines, any pilot or trailing wheels get cleaned by simply using a dental pic to get at any hardened gunk, and then I use a Q tip to do the final cleaning and drying of the wheels.
On drive wheels, I simply put a piece of Handi Wipe cloth over the rails and put cleaning solution on the cloth. Then the engine is put down with the drivers on the cloth and power is applied to the track while holding the engine in place, letting the wheel motion do the work.
If you have an Atlas code 83 rerailer, there is a way to cut slots in the plastic to hold the cloth in place.