Corey's writeup is great.
I prefer a seperate "system" for adding electrical. This way your stock electrics are not touched and potential electrical issues are avoided. Also makes it easier to diagnose future issues if they arise, and create a "beefier" aux. power source w/o dealing w/ OEM wiring.
more:
There is a rubber grommet on the driver's side firewall (green) that you can cut a 'nipple' off and feed wires thru for a clean install.
Use a relatively thick wire (like 10g) from the battery + post. USE A FUSE (15A) or Fusebox as close to the battery as possible. A long, unfused line is potential fire hazard. Thicker wire helps prevent this, as does the fuse.
You can place the fusebox anywhere you like: under dash, under seat, firewall, enginebay, etc, etc
Adding a fusebox is very convienent b/c as you add other accessories, you simply add a fuse and wire to the new fusebox instead of having a bunch of wires & seperate fuses coming off your battery.
Also check the
outfitting section of the forum and search for fuseboxes, adding outlets, etc. There is a ton of great links and various setups. They are on different Cruisers but directly applicable in this case-
Hope my little diagram helps