1.What you do fist is remove the shifter bezel. The black thing connected to the dash/center console around the shifter.
2;Next remove the radio bezel. (Pic.1) Be careful it can break. Use a flat head screw driver and rap some cloth around the end so you do not scratch the dash.
3.Now remove the radio.
4. Follow the climate control switch. The middle AC control. It will connect to the plenum dash pot.
It can possibly look like one of the 2 options.
A. PIc.2 small right metal piece. It looks like a upside down L If it is that one turn it.
B. video 1 pause at 2:24 and look at the top center. Slightly to the right near the hole in the plenum is a kinda round white thing. Remove it and turn it one way or the other. Crank car and turn on ac to test which way is right.
Put everything back together when done.
The video shows you how to pull the dash but the wiring is not easy. My personal experience changing a dash. 2 wires came loose the brake and the turn signals. It took me a few weeks to find the diagram and fix the problem. This does not happen to every one. Just my bad luck. mustang dash removal 1999 2004 - Bing Videos
new engine,1.7 rocker arms,Pipes exhaust, shorty cats , shorty headers,under drive and overdrive pulleys,4.2 upper plenum, throttle body spacer, cold air intake, stage one clutch, shorty shifter, and tune. 8.8 in storage