@Bob posted:You can use a meter, but I'm usually too lazy to get it out. I put about a 1" (length not critical) piece of masking tape on the center rail and slowly run the locomotive over it. If it stops when one of the rollers is on the tape, then the other roller (the one still on the live rail) is not picking up.
Bob, Great tip! I wish that I had thought of this a long time ago. NH Joe