The only difficulty with the digitalization is in the cab cars. Motor and normal cars are exactly like any other EMU from Kato, so I'll miss this information.
But with cab cars I got stuck from the first moment: how to open it?
The key is to begin from the roof, and not from the bottom like all other cars. First of all you have to remove the cabin roof but being careful not to bend the piece because there is the light pick up piece that brings light form the interior leds to the bonnet light. After that remove the roof, windows glasses and seats (unclipping from bottom). Now you will see a gray piece containing led that you have to unscrew to remove.
Once the little circuit with led is in your hands, it's time to prepare it for DCC. The best thing you can do now is to read this marvelous article from Akihabara Station. Thanks a lot!!!!
Basically, you have to desolder one of the led and solder it again changing the leg position. The aim is to join the same polarity legs than your common wire from the decoder. My decoder (Digitrax TF4) has a common positive, so I have to join positive led legs after the existing resistance in the circuit. The other leg of the led (negative in my case) will not be soldered to the circuit because I have three wires for connecting leds instead of two.
Let me do a break: DO NOT USE DIGITRAX TF4 FOR CAB LIGHTS!!!! This decoder has 4 accessory outputs, but none of them is directional depending. If I had searched information in JNS Forum before buying I would have known it but......
You can see the black wire is the positive common (before the resistance), green for green light, and red for red light:
Test it (always test each step of the digitalization!!!!) and prepare the place for the decoder. I choose the end of the car because seats already have like a separation wall. I cut the end of the seats piece behind this separation wall and also the frame in the same position. I also installed interior lights, soldered wires and here you see it ready to close. Closing it is also quite difficult... the light transmitter transparent pieces go out of their place easily:
And here it is with lights operational: