Well I wired up an led in one of my locos, pretty simple cut the old bulb out, install the resistor solder the led in and I'm done. works great very bright. Put the loco in reverse and no light! HA! led's only work in one direction, wire them backwards and they don't work. I guess I dont need lights to back up any way LOL!
If you want the headlight always 'ON', regardless of direction on a DC layout, there's a fairly simple solution. Just put a full wave bridge rectifier between the track power and the LED and resistor.
(https://upload.wikimedia.org/wikipedia/commons/thumb/f/f5/Diode_bridge_alt_2.svg/557px-Diode_bridge_alt_2.svg.png)
You can pick up small package bridge rectifiers at places like Mouser, Digi-Key, etc. Track power connects to the AC (~) inputs. The DC (+/-) side connects to the LED and dropping resistor. Whatever polarity is coming from the track, the polarity to the LED will remain constant.
Len
What is the value of the resistor you are using?
Ton
1k ohm 1/4 watt
That's what i am using also.
But if you think even then that the led is to bright try a 2k2. red red red.
Ton
Since there is a voltage drop through a full wave rectifier, using one to keep the headlight on regardless of direction will also dim the LED slightly.
Len