The jumper wire with alligator clips is another universal electrical tool, second only to the test light. The trouble with these things is, they are so cheap it's hard to buy just one. But that's okay, because you can use a few in different colors. You will want at least one running 6 to 8 feet long with 16-gauge wire, and you can carry that one in your traveling tool kit. You can buy the wire at any auto parts store, and maybe the alligator clips too. You can also buy the clips and assembled wires at RadioShack. If you are assembling your own in heavier gauge or longer lengths, consider also getting the cheap vinyl insulated covers.