There are two under dash wiring harnesses for 1965, the standard harness for indicator lights, and one for gauges. You say that you have gauges which indicates that you most likely had the deluxe (pony) interior. To verify this, you should have a "B" as a suffix in the body style on the door data tag, 63B, 65B or 76B. The other variation would be a GT but with a "C" code engine, that was not an offered option. What's next is difficult, I am not aware of a reproduction harness for a 65 with gauges. Forum poster "midlife" may have something to help.
Jim