I’d recommend the factory service manual rather than Chilton’s or Haynes. Also check out member hatzie’s signature - I believe he has a ton of manuals linked there for reference. I’d also invest in one of those large, laminated, color wiring diagrams, might have to google to find them - but they are available. Someone on here has a hi-resolution wiring diagram for download as well, sorry I don’t remember who it was - but you can google just on this site by selecting the 67-72 radio button above before searching.
EDIT: Here are hatzie’s links, he’s my hero for doing this:
http://67-72chevytrucks.com/vboard/s...d.php?t=558016
And here are some wiring diagrams:
http://67-72chevytrucks.com/vboard/s...d.php?t=185665