If you turn down the audio volume you should be able to hear the constant whirring sound of the smoke fan motor. Does the whirring stop when the engine starts moving? This would at least tell you if power is getting to the smoke unit when the engine is moving.
Did you get to GGG's question about if/how track voltage affects smoke? That is, for the SAME track voltage in neutral or in motion, is the smoke behavior the same? You might try two track voltages in both neutral and in motion, a low one that just creeps the engine, and a high one that really moves the engine.
