Light boards have no capacitors, so there is no need to remove any component. The only needed modification is to make sure that the positive lead of both leds is connected to the resistor. One of them has to be turned for that. The negative lead has to be cut and solder here the white and yellow wires from the decoder as seen in the following photos:
First of all, you need to isolate motor plates from the current pick up plates. The easiest way is using Kapton tape:
I'm using a very small decoder, a Doehler Haass PD05A-3. I found the best position is the one shown in the following photo. Even here, a bit of sanding will be necessary:
Better than sanding the lead piece, if you coot the roof it will fit and nothing will be seen with the plastic piece over the top shell:
And that's all, enjoy!