Make it easy on yourself, there is a spade terminal on the side of the fuse block that has a gauge lights tap, use that. Up near the top, left side.
As far as the battery you need, do some Googling on that part number, not the first time solutions have been discussed on the internet.
AA will work, some guys say no difference. if you are concerned about having the just the right voltage, maybe using a lithium or a watch battery and a variable resistor to drop the voltage will work.
Found this adaptor to use a camera battery in there. Gets the voltage correct. Seems older cameras have same problem, you made need to get a battery holder.
http://www.amazon.com/Battery-Adapte.../dp/B00CTNZ9H0
gg