So, you have a 16-Car, 12-Car, 8-Car, 6-Car or 3-Car consist and you want to get the tail/head lights functioning correctly? Of course, you've already installed the expensive decoder in the engine car of the consist and if this is anything like all of the Japanese models I've dealt with, then it's somewhere in the middle and getting the power to the headlights is not really an option.
Ok, So companies like Kato have created smaller, feature-less decoders specifically for headlight and taillights in end cars... these are still the best option... the advantage to what I'm about to show you is that the lights will switch between backwards and forwards.
Anyway, if you can't, or are morally obliged not to, install the end-car decoders then you can cheat and install an AC/DC rectifier diode to 'fix' the direction of the train (and lights).
This, of course, means that the train you are going to install this into should really be only every traveling in one direction 'prototypically'. You'll be able to swap the end cars when you want the train to travel in the opposite direction, but this could be tedious and so it is entirely recommended this method only be used for consists where you intend on running them in one direction.
Micro Ace 6-Car "あいづ" KIHA 485系
So, as you may have recently seen, I installed a decoder in my 6-Car "あいづ" KIHA 485系。 The engine car was number 3 of 6, so couldn't really get any further into the center... which is a good thing as it means it's nearly pushing as much as it has to pull.
So, I decided as I'd got it at a bargain price, that I wasn't going to fork out too much to make it DCC. I had the decoder in the engine car and wanted the lights to not 'buzz' and function correctly. I intended on having it running in one direction most of the time and could handle swapping the end cars if I wanted it to go the other way.
What this meant is that I would get an AC->DC Rectifier (0.84c at the local electronics store) to convert the AC voltage off the tracks to DC.
Once in DC voltage the polarity would be fixed... even if the car was swapped around on the rails.
Right, so I removed the old lighting circuit board and bent the pins up that connected with the power rails... I then extended the AC side of the rectifier and pushed the pins into the area where the old contacts used to touch the power rails.
I then soldered up the DC output to the circuit board and threw it on the tracks to test.
Ok, this worked well... the lights even stayed on constantly after a bit of a wheel clean. Unfortunately, you now cannot 'shutdown' the train in a siding without cutting the power. The other issue now was that the rear car would have the 'Forward Lights' on as well if wired up directly... I therefore had to reverse the wiring after the DC output. I used my 0.25mm 'winding wire' for this.
And then a test...
And that was it... the train was DCC'd and ready to roll... It worked perfectly after this as well.
I then quickly slapped a Rectifier in my Twilight Express end car and disabled the lighting in the car that sits right next to the engine.
To my surprise... a 12v BULB!... This must been an older set as Martjin had previously mentioned.
...and that was a wrap... yes, it's a mighty cop-out... and those who wish to have functional/switchable head/tail lights should not do this, but it does work and I must admit, does the job for my kinda running (Full Steam Ahead!)