With a 44:1 gear ratio, you can make this one really crawl. FWIW, I use the MTH tethers for TMCC upgrades as well, gives me plenty of pins. As for the smoke, I use MTH steam smoke units and mod the resistors for TMCC installations. Of course, I use them with the Super-Chuffer II and the Chuff-Generator, so I have power for the fan motor.
If you want to put an LED in there, consider a 470 ohm resistor and a bridge rectifier off the motor. The bridge rectifier will maintain the same polarity all the time to the LED, and the 470 ohm resistor is suitable for at least 12V on the motor.
I hope you don't mean the MTH electrocoupler, unless it's the PS/1 coupler. PS2/3 couplers are NOT compatible with TMCC coupler drive, they're much too low impedance.
