Here's the schematic for the project diymagicmirror.com/files/schematic.pdf
You just need an Arduino and can wire the schematic using a breadboard.
If you require a more permanent installation than a breadboard, the Magic Mirror Arduino Shield can be used. The switches and sensors are wired to two standard cat5e cables (T568B wiring) that plug into the Shield. Referencing the manual diymagicmirror.com/files/building_the_sensor_hub.pdf
for the Shield, it will tell you what color wire goes to what sensor.
There is a kit available from Seeedstudio which includes the Magic Mirror Shield, necessary components, Seeeduino (Arduino clone), and the Magic Mirror software www.seeedstudio.com/depot/diy-magic-mirror-p-606.html