ok, well, a fuse is a part in the line of the wire. when the car is turned to "on" and the fuse is taken out, you take a 12volt tester, hook up the ground of the tester to anywhere close, and you take the positive side of the tester, or the prong, and put it to one side of the fuse outlet, if it lights (mine has a light that lights up), thats the side that delivers the power. if you do what i just said, and the tester doesnt light, then thats the side that you wanna fuse tap on. this way if something goes wrong, the fuse will pop. if you hook it to the side that gets the power, you could mess up whatever runs its power thru that fuse.
thats the way i think it is. i havent fuse tapped anything in a while, so it could be the other way around. but ill double check tomorrow and let you know, unless someone reads this between now and then. but yea, ill check tomorrow for you and let you know. but im pretty sure i got it the right way.