I just did the dome light on my truck that only had the one purple and white wire. For the MUD UK dome light (I'm actually doing s review for Lucky8 on this) I grounded the unit to the base for my light using the grub screw that held that glass cover on and didn't use the door activated wire since I don't have that feature. As I have an internal roll cage I had to fab up a mounting box as well. In the end I am very happy with the results. I had already ran a red LED strip for the second row and the MUD UK unit is just far superior. All in all this is well worth it. The ability to have red and white at the flip of a switch in a convenient location is really nice.
Here is my baseplate with the ground wire attached to the grub screw.
here is the box I used to mount the unit.
This is my original strip light and what it looks like at night.
Here is the MID UK red light
Here is the MUD UK white light