This is an original heater/ac/defroster relay for 1973 Mustangs and other Fords.  This part is located up and under the dash and mounted to the right side metal defroster flange.  Part # D3AF-9E447.  For those demanding original Ford parts. I combine shipping on all my parts.  If there is anything else you are in search of for your Mustang project, message me.  I just may have what you need. I guarantee all my sales.  If there is anything you are not satisfied with, let me know.  I will take care of it.  Please leave me positive feedback if you are happy with your purchase.  If not, contact me and I will rectify it.  Bob  631-833-0305 Additional keywords;  Mach 1, fastback, convertible, coupe, GT, Shelby 350 500, Grande