It takes a second to look at the fuse box given in most of our rangers but you'll notice there's some good ports that you can use that ford has left open. The trick to this is, a lot of the connectors behind the box itself are connected with a bridge, find one that isn't in use, cut it off, wire and solder it to whatever you need, plug it into an unused port with an amp level that you need (also, Key-on/Key-off if it matters in your case).
I just installed a trailer brake controller in my 99 and wanted a key-on/off and found that in this case, fuse 16 has a power link it shares with fuse 12 which is open. Like I said, find an extra terminal that you arn't using, snip it out, reuse the terminal and solder it to the wire you need power to, and plug it in the spot you need.
Now fuse 12 controls my trailer brake controller and is a lot cleaner than just wiring directly to the battery. Also, make sure you're not going to overload the factory wire that you're using to bridge it with here, always do your research, test for amps and volts to see how much power is being drawn from the wire before you install your aftermarket device so you don't demand too much power from a wire that cannot support it and end up burning the wire which can possibly start a fire.
But done right, you will have a clean install! I'll do a picture write up later on. Right now I'm still cleaning my wiring up a little more and finishing installing, but it works for right now. If you take the fuse box apart, I'm sure that some of you can figure out what I'm talking about.