David,

There are a couple of diagrams, depending on where you look. I have linked one that shows wire gauges pretty well. Your choices are 18, 16, 14 and 10 gauge...although not crystal clear, they are discernible (to me) and you can kick the magnification up to 200% if you need.

If it's the same one you found, dump it and someone else might be along with a better one.



http://chevy.tocmp.com/electrical/wiring/pdf/54truck.pdf

Stuart