In front of the radiator there are two little boxes, one on the right side and one on the left. Take a 3-lbs sledge hammer and smack the one on the right real hard. That'll disable the airbag!

J/K
You can pull the fuse, but there is a capacitance charge to the system so give it at least 15 minutes after you pull the fuse. Under the dash on the glovebox side is also the airbag power module that you could unplug to completely disable the system.
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Jeff Chambers
1990 Mustang GT 10.032 Seconds / 137.5 MPH
14-time Street Warrior World Record Setter
CRT Performance
2001 Tropic Green Mustang GT - 12.181 / 113.2 MPH
2002 Ford F-250 Crew Cab 7.3l Power Stroke - 17.41@77.2
"There's nothing boring about a small block automatic shifting gears at 9400 rpm!"