The following information was obtained from the '1970 Ford Trucks Body Builder's Layout Book' which I borrowed from 4x4x4crewcab for scanning purposes, to be posted later to the site. (I'm ALMOST done with it, Mark!)
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The following wire chart suggest wire gages for various maximum current draws and will aid in the selection of the correct wire size. The current capacity of a given wire varies with temperature and type of insulation, but the following values are generally acceptable. The values listed are the maximum current capacity for plastic-insulated copper wire:
20 gage - 10 amps
18 gage - 15 amps
16 gage - 20 amps
14 gage - 25 amps
12 gage - 30 amps
10 gage - 45 amps
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Now, on to your original question. The following is a chart scanned from this same book. I'll be including it in HTML format on the site sometime in the near future for easier reference, but in the meantime, you can use this:
This chart also shows some circuits only found on the heavy-duty trucks, but everything in the light-duty trucks should be here.
Hope this helps.
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