Maybe it's just me, but it seems like fuel system accessories were often mounted in this general location, on the driver side wheel well. Mine has a spare inline fuel filter mounted in the same spot
I can't say
what it is, but it looks like some sort of backflow preventer or maybe even a really weird pressure regulator. Not sure why a fuel system would need either of those things... Maybe it was a brake accessory? Now that I look more closely, is that a wire coming out the right side?
At any rate, you can tell it has been sitting isolated for a long time since the threads were sprayed blue during the repaint your truck seems to have once gotten. Given that, you can probably rest assured that it just an old obsolete part.
If you take any more photos or figure out what it is, do share.
And regarding your wires to nowhere, print this document nice and big, and field-verify the wire runs you're confused by:
http://www.luvtruck.com/PDF/Series2.pdfI used a few different colored highlighters to keep things organized.
It looks chaotic but it's a smart diagram - laid out like a truck from above, making it relatively easy to figure things out.