i would say to try and rewire with the same size that you took off because different circuits call for different size wires depending on the load that they carry. there are a lot of factors to consider i.e. how long is the wire on the circuit vs how many amps it is carrying, how big is the load, what size fuse, the sizes probably range between 12-18gauge. for what is was worth that my opinion good luck
I concur with Stretch, there are a lot of variables. Are you re-wiring the entire rig? I just finished re-wiring with a painless kit. It's not easy 1 2 3 as they say but it is something do able at home. I did mine in the parking lot at my apartment. It took about 4 or 5 good days to do.
You can call Painless and ask for a fax of the wire identifyer for the FJ40 kit. That will show you what gauge wires they use and fuse sizes for all the circuits. Good luck.
IMO, no smaller than 16....IIRC, most circuits on a Cruiser are run via 18 gauge, but some started-switched stuff runs as much as 12 or even 10.
I run 6 alternator to battery (marine fine strand), 0 weld cable from starter to battery, and 0/2 (thumbsize) weld cable to the winch. Electricity runs on the surface of the wire (so I understand) so the finest strand stuff offers the least resistance. (winch/starter/alternator are the critical ones for this)
#14 will do just about all you want. think of a medium duty extention cord. Most medium duty will handle drills and such pretty good at 25 to 50 feet and they are 14 to 16 guage. A motor is a heavy load so in the short distance on a cruiser 14 is fine and is still small enough its not a pain to deal with. I use 14 for any fixes on my cruiser. The only time you might want to step up to a larger size is for motors and long distances. You get a big gain in just a 2 guage step. And in case some of you are wondering the smaller the number the LARGER wire size. If you plan on doing you own wiring think about the insulation. try to get thick insulation because it tends to wear off over the years on 4x4's. Use some kind of protection when going through holes. Heat shrink is a good thing to have for any kind of connection. well sorry if you knew most of this but hope it helps if you didnt. And dont let people fool you about electrical work. Its not magic. its just wires. its not that hard to work on.
Anyone contemplating rewiring using painless or other can benefit by reading "Automotive Electrical Handbook" by Jim Horner availible at Borders or just about anywhere. Definitly worth the $15.00 price of admission.