When I had them on my Miata, I wired them to my parking lights. I tapped into the possitive of the driver side parking light wire. They sell taps at Home Depot. I would have been hesitant for something you cannot remove. On the miata there you screw them down over the factory, so you can take them back off (which I did when I sold the miata). Was there no option for that?
I had the joy of experiencing running wires from the cabin, into the engine bay last weekend when I installed my amp. It is no miata. Infiniti REALLY believes in insulating!

I had to take off the driver wheel, and then there is a passthrough for the engine bay, and then the driver cabin. It would be perfect for running the wires you need to connect the leads to the parking light. If you know which wires work for the existing gauge set, go for it! but like what was said before, the research could be hidious.
-Robert Cole Birmingham, AL.