I tried out for my high school play years ago because there were a bunch of cute girls in it, and a few of them told me I should. The problem was that they were too nice to tell me my singing wasn't all that great. I don't know if they knew I couldn't sing and wanted to embarrass me or what, but as it turns out I'm tone-deaf and should be kept miles away from any karaoke machine.
I found a phone guy working on the phone lines at the Crab Shack, and I thought he was listening to some weird music, but, hey, we all have our unique likes and dislikes and I didn't get it, but I hung out and listened for a while. After I was there dancing to his music for a little while, he turns to me and says, "What are you doing?" I tell him I'm trying to enjoy his music, he looks at me kinda funny, and then he explains to me how he uses this tone-generator can to figure out what wire is attached to what over long distances.
Oh, I tried out for the play and did horribly, and everyone was laughing at me, and I'll never forget it. So anything now to do with tones, singing, or anything like it I try to stay far far away from. It really is something that will haunt me forever, but even with the bad memories and as tone-deaf as I am I like using tone-generators to trace wires.
The packaging of the one I used the other day calls itself a "classic tone and probe kit" and has two parts. The tone generator creates an electromagnetic field in whatever wire you clip it to, and the probe picks up that field and puts it into a speaker that makes an audible tone you can hear.
It isn't a cheap tool, but even as cheap as I am, I think it is well worth the price since it makes finding and identifying wires so much easier than anything else I've used. Sure it isn't something that a lot of automotive guys use so I got to thinking how I should show you guys how great these things are for tracing wires in Jeeps or anything really.

The phone guy told me that...

The phone guy told me that he liked the Progressive Electronics units the best because the tone generator seems to generate a stronger tone, and can be picked up further away than other units. Both the generator and the pickup use a 9-volt battery, so you will need to pick up two of them in order to get going.

This is the generator box....

This is the generator box. By clipping this to one end of the wire, and then probing downstream you can easily see if there is a break in the wire or a bad connection. It works like a test light, but with sound instead of light. Sometimes you will need to disconnect the wire to avoid wrong results.

Once you have the tone generator...

Once you have the tone generator clipped on, it is a simple matter of probing. It is better than a continuity tester because you aren't limited to the 2 feet of test leads that you normally get, and don't have to extend the probes. The probe is wireless and you just test the wire until you hear a sound. It really is that easy.