its rather easy to set up. run power (with fuse) from constant 12 volt to light
run neg on light to swtich (same type as door switch for interoir light)
done those switches you can get for a couple o bucks if that and they self earth when they are realised up.
i installed a red neon for the interoir light on my ke70 when mine origanal failed on me.
i just screwed it into the roof lining and hid the wires as much as i could. trim would be the biggest annoyance