The lamp outputs from most TMCC stuff, including anything that uses the R2LC or R4LC are half-wave track power in command mode and full-wave track power in conventional mode. Typically, for incandescent bulbs, a 12-14V bulb is used. If you want to use an LED, a series 470 ohm resistor is a good choice.
The headlight on the steamer should be on all the time, the tender reverse light comes on in reverse. That is accomplished by using the AUX1/4 configuration code, steamer with smoke.