The MX-5's interior is known for it's minimalist nature, and with that comes the poorly lit interior. Vlad from Jass Performance has come up with a neat solution and below is my installation, with a slight difference.
The kit comes supplied with instructions and is plug and play.
Firstly, you'll need to remove the visor and roof latch. This'll allow you to mount the light and tuck the wires away.
The passenger and driver side lights mounted up and wires tucked away. It's a little bit tricky to do, try have someone else around to help out.
The black wire has a small ring terminal which screws into your existing courtesy light, this just allows it to turn on with the doors and still give you the ability to switch them on/off whenever you please. My install is a little different to the standard instructions, I've added a plug and soldered the red wire directly to the factory light. So please note that soldering is NOT required.
And a quick photo to show how much coverage it has. Photo was taken without flash and in complete darkness.
Second photo below was taken using a higher ISO setting on the camera, again no flash and in complete darkness.