It is entirely possible that it does not go to anything. A lot of these cars got the same harness regardless of the options on the car. So it may be for something not on the build sheet for your car.
DO you have something not working? If everything is working, then don't worry about it and tuck it up out of the way.
I took the dash out to replace the heater core, n just noticed that there was a connection available. I guess I will find out when I turn the car on when I finish the Cobra MC n booster upgrade. Plus, install the Ac hoses.