Originally Posted by Fronty Owner

output wise your right on the truck (actually can be closer to 15 volts as a 12 volt lead acid is 13.2 volts)
Internally, an alternator produces a 3 phase alternating current voltage source. then its rectified and regulated to the output you get.

I have seen a couple kits that bolt onto the engine that will put a 240 volt service output on your truck.
Alternatively, some old school (50s?) car generators I believe would output an AC voltage that you then run thru an external regulator/rectifier.