Open your door, and look under the dash at the fuse panel. Near the top of it will be some "ports" that have nothing plugged into them, that a fuse won't fit into. More than likely, there will be a couple of them with one wire plugs into them already though. THOSE are accessory plugs.
No, you probably can't get them at pep boys, although I guess its worth a look if you don't have any 'yards close by. The plugs are specific (they are actually "keyed" by color IIRC) depending on "when" they get power. There will be constant 12v, ignition switched 12v, and perhaps accessory 12v. (key position "ACC")
There is no simpler way to do a GOOD job of wiring in accessories than using this method. There isn't much worse than a mess of tangled, poorly done wiring additions both in troubleshooting problems and in trying to mess around under the dash. Reason I mention pep boys likely wouldn't have them is because the local chain stores don't even carry solder. No wonder so many vehicles have piss poor wiring modifications in them... "well, they don't have solder, we'll just use these splices instead!"
There are even factory accessory plugs that allow you to "piggyback" MORE connectors on them, should you run out of dedictated spots.
