For 1966, the Fastback featured a redesigned grille, new instrument cluster, and newly styled wheels. An automatic transmission became available for the “HiPo” V8. Side scoops were absent on the GT model, making for a cleaner look while driving lamps were offered as standard equipment. In addition, the GT featured side racing stripes which took the place of chrome rocker panels, giving the vehicle a serious performance racing look.
At the time, Ford touted exterior styling features, of the Fastback, such as a unique roofline with swept back appearance, functional air vents in the roof's rear quarters, and a large rear window integrated into the curvature of the roof's sheet metal. Tinted glass in the rear was standard.
Although other Mustangs in 1966 sported the Mustang Pony emblem directly behind the front wheel wells, the GT Mustang featured a special GT emblem in its place. In addition, the letters “MUSTANG 2+2” were added to the lower front fender on the Fastback. The 1966 was also the first year Mustang featured standard backup lights.
On the inside, Ford offered a fivedial instrument cluster with fuel, oil pressure, amps, and engine temperature gauges. In addition to a rear folding seat, the Fastback models included dooroperated courtesy lights, a large panel mounted ashtray.