First off, a visit to Halfords (naturally) to get some more wire and some attachments. I then attached one end of the wire (blue this time - no black available) to the neutral terminal on the battery, and ran it the length of the car through the same holes as the existing wiring, through the engine bay and out into the boot where I attached it to one side of the light.
Next up, run the red wire from the switch, back through the car, through the.. oh. Ran out of wire.
Back to halfords again for some more red wire.
And.. through the engine bay and into the boot and the other side of the light. Tighten up all the little connectors, turn the power on and flick the switch. Nothing seems to have melted, so check the light and wow, it's on! Two successes in a row, this is unheard of.
Now the fun bit :-)
I've seen pictures of other MR2s so have seen they put the light into the rear light valance thing so I took this off and the light fits in the gap. Just need to drill out the plastic and screw it in place. Luckily I seem to have one of those big gap drill bit thingies (a serated disc type effort), and it appears to be exactly the size I need by some bizarre concidence.
So drilly drilly, and before you know it, this light is in place (although it was a bit of a pain as the back was not flat for some reason) and everthing is done. Next!
Quite bright - this was taken in the sun, at night its much brighter.