I take it that you don't have an owner's manual or a shop manual or an assembly manual. They all have wiring diagrams in them.
Here's one from another forum.
http://67-72chevytrucks.com/vboard/showthread.php?t=308536Scroll down to post #4-the second link in the thread.
I printed a section and you'd still need a magnifying glass to see it, but without one, you can see the yellow wire goes to fuse panel and the blue wire to the switch. They both connect to the wiper motor.