With TMCC you only have one item you can control independently, either smoke, cab light, or mars light. If you want to keep control of smoke you have to build your own independent circuit. A fairly easy one is put an amplifier (op amp) that senses motor voltage. When voltage is applied to the motor and the engine is moving the amp opens a relay/switch, that turns off power to the cab lights.
One of the many drawbacks of a closed system like TMCC/Legacy is the difficulty of adding your own features unlike DCC where decoders and controllers will allow you to add many.
Pete
