maximum length of wire?

You won't start a fire by using 22 ga wire, but it is marginal for voltage drop in when used in a bundle or in any conditions that are subject to extreme temperatures, such as in an auto engine compartment or under the carpeting/floor mat. You'd be safer by using 20 ga wire. If the wire is only going to be a few feet (10 feet or less), and used only in the passenger compartment, then your 22 ga wire is probably OK. If the wire isn't going to be exposed to the extreme temperatures in the engine compartment, then you might consider plain old AC zip cord. It comes in several sizes; 18 ga is usually used in small household appliances and can be purchased by the foot in home improvement centers (home Depot, Lowes, etc), hardware section of department stores (Walmart, KMart), and in auto parts stores. If you go that route, be sure to get the variety that has a rib on the insulation of one of the conductors, or different colored wire so you can identify the wires. Most AC extension cords have either or both. Also, Radio Shack used to stock many different kinds of wire.

If the wire needs to go into the engine compartment, be sure and get high temperature wire. Auto parts stores would be the place to start looking for that.

I don't want the wires to start melting and cause a fire!

if you're connecting directly to the battery use a fuse near the battery. 2A wopuld be a good size.

make the cable as long as you want so long as your video equipment can hnadle the voltage drop (10s of metres atleast) and the wire isn't left coiled under a blanket.

bye

Agreed, but then you'll get people moaning that crossposting is wrong. They usually give some silly reason like not wanting their posts to go to "that other group" (said with furrowed eyebrows).