On the way home tonight all my gauges and radio quit working. When I got home and turned the truck off it wouldn't crank back up, just clicked. I jumped it and noticed the volt gauge was on the low side. I pulled the negative cable off the battery and the engine quit. Do I need a new alternator or could it be something else? Can I replace the voltage regulator on an 04 Ford F150 or should I just do the whole alternator?

Try removing and fully charging the battery--it may be that the alternator is okay. Many auto parts stores will test and charge batteries for free. They will also test alternators for free. It wouldn't surprise me if the battery needs replacing.