I had a 89 GT that I installed the 130 amp polished PA alternator on. It worked GREAT!! I had 2 14" electric cooling fans, a MSD box, 2 fuel pumps and a programmer. The gauge never went below 13 volts. The instructions say that you might have to clearance the alt bracket for the alt to fit.. I did not! The area that they are talking about is casting flash and there is so little there, that even if you had to file it down, it would probably take one minute to do. I highly recommend the upgrade wiring option. The alt came with the connections and terminal eyes to install it and literally took 10 minutes to due the install. The alt is rated with and already has a underdrive pulley on it. Bottom line... if you are doing a big stereo, or you have a lot of electronics on the car..these are a huge upgrade and with a life-time warranty they are a very wise investment for your Mustang!!