I have a 02 mustang base v6 5 speed. There is a part behind the passenger skirt that looks like a horn but has a vacuum? Line attached to it. It's near the ccrm. I just bought car and took off fender to find it broken and not attached. I'm trying to see what it is so I can order a new one and get it attached. Thanks

 

Sounds like your Vacuum Reservoir. These normally set between the inner and outer fender. Do you have any issues with your HVAC output when not set to defrost position going to the defrost position during acceleration or staying in the defrost mode? If so, then it's definitely your Vacuum Reservoir.