the buckle and unbuckle 9 times method worked in my 05 and my father's 04. You do have to do it for both front seats though.

 

you just have to not go so fast when buckling and un buckling the belts i have a 12 f150 and it took me about 5 tries this will work on almost any form mustangs and others we have done this too.

if it does not work vary the speed you are buckling