I examined the DCC/DCS switch on one of my Premier MTH diesels and the wire to it is indeed black, not gray. I found the same black wire on my Aerotrain and clipped it, that did the trick! the gray wire I cut has something to do with the speed control/momentum of the locomotive. The train will operate with the gray wire cut but it tends to have rather quick take-offs. I reconnected the gray wire and now I have a nice steady, slow take off.
Joe