Fitted with Fx - 12v Flexible Lighting Strips (from TrainAidsA). These models come with factory fitted interior lighting but I was very unhappy with the yellow LEDs as it did not look realistic. Replacing the yellow LEDs was going to be too much hassle and one yellow LED needs to be left in each coach to provide light to the destination board on the side as the text on the real ones is yellow.

In order to keep things simple I fitted the Fx - 12v Flexible lighting strips over the top of the Fleischmann LEDs. You will need a strip of 6 LEDs at the front of the car and 3 LEDs at the rear. Make sure you do not cover the single LED that lights the destination board but you will need to prevent the yellow light from leaking into the rest of the coach. I achieved this with some black insulating tape. The new LED strips were fitted with a 1k resistor to reduce the brightness and the wires were soldered to the metal strips at the front of each of the cars. By doing it this way you loose the ability to switch the interior lights on and off with your DCC system (You can still switch the headlights on/off) but I personally do not use this function.

A way round this would be to wire the new LED strips to the green and blue wire outputs from your DCC decoder but as both of my railcars have sound fitted I did not want to invalidate the ESU warranty.

Fitted with S12WW: Warm White 12v Lighting Strips from TrainAidsA. Each coach has two and a half strips on the top deck and one and a half strips on the bottom deck. These have been fitted with a 1k resistor. To stop the lights from flickering I have through wired the coaches using Roco Current Conducting Couplers (Part Number 40345) so that the coaches pick up from 24 wheels on the 5 coach set. (The Roco couplings can be seen in one of the close up photos of the bogie).
Only the driving trailer came fitted with pick ups so I built some new ones on 2 other coaches using PCB board and phospher bronze strip. (TIP - Use the smallest diameter available as mine had a habit of sqeaking when I first tried this.) These are relatively easy to make as the wheels have a shoulder at each end of the axle for the pick up to rest on. It is just a case of drilling two holes either side of the axle and feeding the phospher bronze wire through this. (See photos).

The other problem I encountered was voltage drop on the 5 car set which resulted in the end cars being significantly brighter than the lights in the centre car. To solve this I fitted pickups to the centre coach as well so that cars 1, 3 and 5 supplied the current to the coaches.
There is very little room to run the wires through the coach. I glued some small diameter wire under the lower deck interior but it is a tight squeeze. It is best to start with this and then solder the wires to the bogie pick-ups rather than the other way round.
 
One small problem with lighting coaches is the need to detail the interior.

A word of warning... 5 Double Deck coaches need an awful lot of HO scale people to stop it looking like an empty coaching stock working! Trust me as I have spent a small fortune and they still look empty. However it's a small problem in comparison to the complete transformation of your day time layout into a night time heaven! The great thing about night time running is it hides all manner of modelling mistakes!

Fitted with Fx - 12v Flexible Lighting Strips (from TrainAidsA). I have not used a resistor as the windows are tinted and having seen the prototypes in Germany the interior lights are quite bright on the real ones!!!

The lighting strips have been cut to 9 LED lengths in the end cars and 6 LED lengths in both the centre cars. Roco have provided solder points to attach the wires near the decoder sockets and then wires have been soldered from the solder points on the lighting strips between the cars. As this set is articulated and cannot be split there is no need for connectors between the coaches so you can run the wires from one strip of LEDs through the articulated gangway and solder it directly to the next strip of LEDs.

The instruction booklet provided with the Roco model explains where to attach the wires. (Please note that in German interior lighting is Innenbeluchtung).

Fitted with S12WW: Warm White 12v (TrainAidsA) Lighting Strips. Each coach has 2 strips connected together. These have been fitted with a 1k resistor to reduce the brightness to better represent the real ones. I have also painted the interior walls an off white/cream colour that matches the real coaches as this helps to brighten the interior rather that highlighting the black walls that Fleischmann provide.

To stop the lights from flickering I have through wired the coaches using Roco Current Conducting Couplers (Part Number 40345) so that the coaches pick up from all 32 wheels. It can get expensive but personally I think it is worth the cost.

The S12WW lighting strips are a big improvement on the Fleischmann lighting kits as they only have one bulb in the centre of the coach which doesn't look good and isn't helped by the prototypical tinted windows. I have however used the original Fleischmann Pickups on the wheels and whilst not perfect it's easier than building new ones.

Fitted with Fx - 12v Flexible Lighting Strips. Happily this is a nice and relatively simple job. The hardest thing is getting the body shells off without damaging them!
 
Trix have provided pre-fitted wires for interior lights so it is simply a job of connecting the two black wires to the LED strips. I have fitted a 1k resistor to reduce the voltage.

A modification I have made is to through wire the unit so that it picks up from both the front and rear cars at all times. In doing this the lights are less likely to flicker and if you are using a DCC booster section the train will run through and not grind to a halt.

To do this you will need to solder jumper wires from the brown and red wires on the end of the circuit board of the centre car. These two wires are then run along the length of the centre car and soldered to the brown and red wires at the opposite end. (Brown wire to brown wire, red to red). These connections can be found at each end where the wires come up from the couplings. (Make sure that the original wires are still attached to the solder points of the circuit board as well).
 
However you cannot do this if you are using an automatic stop section on your layout (where the trains stop automatically in-front of red signals).