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69, 350/350 w/AC
I have 4 wires that USE to go to a relay mounted under the windshield wiper door canister on the right side of the engine compartment by the heater/AC coils. I think the relay is for the AC, but I don't know. There is a small blue wire, small black wire, a big orange and a big purple wire. They are all spade type connections. I cant find it on my wireing diagram ...that's why I think its for the AC.
I think I found what your looking for ! Google (Index of/johdotukset) This site is worth it's weight in gold for wiring diagrams. It has corvette wiring diagrams for 53 to 82 by year. When you get to the site , go to the 74 wiring diagram & scroll down to the bottom. There you will find the AC diagram with the wire colors you described & where they go. It's a PDF file. These PDFs have save me hours of searching for diagrams. I printed every year & put them in a book so I have them when I need them. I have 3 C3s & plan on having more so I'll be needing them.....Good Luck