Ive done the swap before, you wanna get a harness from an 89 Mustang, its plug n play, no left over unused plugs from the would be airbags and etc from the 90 and up models Is your car a 5 speed or auto, it is specific on some computers. I believe an a9P will work with both which is what i used, because i also did a 5 speed swap. If yours is a 5 speed a9L is what you want!!