Virtually all the brass locomotive Seuthe smoke units are a 6V rating, and the regulator used will invariably be a 6V regulator.
Give me a toot if you need a replacement Seuthe smoker for that locomotive, I have few of them. As others have said, the backup light is likely to be an incandescent and not an LED.
You can test the Seuthe smoke unit by applying 6 volts, AC or DC to it. However, do NOT put more than 6V on it, that likely will kill it. You can also just measure the resistance of the smoke unit, the 6V one should have about 7 to 8 ohms resistance if it's good.
