Most people use an opening on the passenger side door with a rubber grommet over it. Look through some of the "complete installation" posts here and they will show where it is.
-Remove the passenger front wheel or turn your wheels all the way to the right (its easier to just take off the wheel).
-Remove liner in wheel well
-Close to the bottom will be a grommet with a wire going into it and a little nub
-You have two choices here, cut the tip off the little nub (what I did) and run the wire through or push the whole grommet to the side and run the wire through.
-Check for wires coming in on the passenger floorboard, you should see the grommet from inside as well, feed the wire through with a hanger or something similar if you're having trouble.
-From the battery or relay box (whichever you connect the power wire to), there will be cutouts on the very edge of the engine bay (right next to the fender). These run right into the wheel well so you can route the wire right into there for a clean look.