I had one years ago on 63? T bird. Couldn't find it. It had the older analog clock that had points. When the clock spring needed to wound the points would close, wind the spring and the points would open. OK but this clock wasn't working so I blew by it. After chasing my tail for a few hours a buddy suggested disconnecting the clock. I said why? it's not working
Well lo and behold the points were stuck shut, which overwound the spring until it broke, so the clock motor was running all the time. But you couldn't hear it and I ASSumed it was not the issue.
might try the bulkheads as suggested as it might narrow it down. I would start with the wiper motor harness.
It has to be something that is hot all the time and not fused by the fuse box
A schematic would be very helpful as well
Keep us posted