Robert, I assume that you have one of the older, Pop-Top 23s, with a keel/Centerboard?
Anyway, the wire that you describe sounds like a previous owner installed a topping lift that would be adjustable at the boom-end using a length of line from an eye on the end of the boom up through that block and down to a cleat on the boom. Is there another small block near the end of the boom that the topping lift adjusting line would feed through? Then forward to a cleat?