Headlights and beacon for the rear cab
The headlights are actually set up as warning strobes, just as on the real monorail (as of 2017, it seems to change frequently).
The rear cab gets batteries (2xAAA) and a voltage converter to provide the 3.3 V required to light white LEDs. The roof beacon is yellow, as are most I have seen at WDW. The flash pattern is controlled by a PIC 12F1572, my "go to" microcontroller. Two quick flashes of the strobes followed by a longer blink of the beacon, repeat.
The Mark VII rear cab has a "pocket" for the lights, we just need to drill holes for the LEDs. The WDW model as shown here requires us to cut out an area for the headlights, I have a filler panel (with holes for the LEDs) on Shapeways (for sale at my cost). https://www.shapeways.com/model/upload-and-buy/6559585
And since there is so much room in the rear cab, and since we now have power to run some electronics, we may as well add a decent audio system! By decent I mean one with good sound *and* the "por favor..." message!
Adafruit's audio FX and 2W amplifier produce the sounds, up to 10 messages and up to 2 minutes of high quality audio. 16 minutes is an option. A larger and improved speaker delivers the sound. Messages start about 10 seconds after the previous one ends, either sequential or random.
The Disneyland Mark VII version in action: https://www.youtube.com/watch?v=B0kRHZ4qhjg