It's pretty easy to figure out which wire does what. Just take and plug things into the harness and try them. In 10-15 minutes you'll have it all figured. Like I put one wire in and tried the turn signals and the horn went off. That told me which wire from the switch was for the turn signals and which in the harness was for the horn.
If someone's got a diagram I'd appreciate a copy too. I just got a '71 F100, and the turn signals only work with the ignition in the accessory position. The previous owner recently replaced the ignition so I'm guessing he may have wired something wrong, but I haven't figured it out yet.
edit: Well I was messing with the ignition, I had pulled the tumbler out and was fiddling with the wiring in the back. Then I heard a "hissss.....POP!" and got that nice smell of burnt wiring. The wiring on the back of the ignition got really hot, especially a thicker yellow one, and of course the truck no longer starts. I then realized I had gone from non working turn signals to a non working truck. ugh.
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