10 or 12 guage should work. I have an Alpine 9813 and on the Crutchfield site and some Ebay sites it says Alpine states you must use 10 guage wire. I did not find that anywhere in the owner's manual or on the Alpine website. But the stock wire is smaller than that on the unit, so be safew and run bigger wire. It's cheap insurance.

 

I have mine hooked up tp the fuse box. There is a constant 12volt hot spayed connector that is not used on the left side of the box. I believe it is the middle of three. (have not looked since I hooked it up) I have had no problems.