http://arrc.epnet.com/autoasp/index....ain.autorefctr
I don't know what year your car is, so I put in 1990 Mustang GT. You'll see a table of contents. To get to the instructions, pick "Repair Procedures", then "Chassis Electrical", then "Air Conditioning", then "Evaporator", then "Removal and Installation". It should take you to this, but for the year YOU put in.
Sorry, that's the best I can do.
Bob