Lionel Legacy K4 and other steamers use a 3mm LED without shoulder. They not only provide a bright headlight but also, due to the lack of a shoulder, light up the number boards.
Does anyone know if Lionel incorporated a resister in the Legacy boards or was an additional one added to provide the proper power to the LED.
I was thinking about replacing the grain of wheat bulb in my M1a and substitute the Legacy LED. The headlight assemblies are identical in both the Legacy K4 and the PRR M1a.