The year 1966 proved to be one of the most successful years for the Mustang that Ford was yet to see. Many people looked forward to the new upgrades, luxury, and performance that was beginning to be added.

Ford Motor company had expected an annual sale of roughly one-hundred thousand cars in the Mustang's first year. High expectations did not hurt them this year. Outstandingly, more than twenty-two thousand Mustang were ordered on their first day. The sales shot up eventually reaching four-hundred seventeen-thousand cars sold in the first twelve months in their debut. This presented a high standard for the next year to come, but little did Ford know how high. One million Mustangs were sold by only March of 1966 alone. More people began to recognize the Ford Mustang as a car of power and performance. This car appealed to both types of people: those who desired daily drivers and those who wanted a sporty, weekend, show-off car. The Mustang did not take long to rise above and beyond in such a short period of time.

Ford Motor company, in the year 1966, saw advanced fine-tuning of the Mustang. The Mustang was finally breaking free of its Falcon influence starting with the new gauge clusters they introduced. Two and four barrel editions of the 289-ci V8 then replaced a 260-ci V8. Even though the racing image of the Shelby GT-350 carried thus far was being spoiled by the new addition of an automatic transmission, the GT-350 was still attainable. The car also came with a variety of four colors and had an option of a Paxton supercharger, that could boost horsepower with a result of almost forty-percent difference.

The total production amount for the year of 1966 was a total of 607, 568. The standard convertible was sold for $2,652. The standard coupe sold for $2,416. The standard fastback cost $2,607.

This '66 Mustang was highlighted by a few new adjustments that made a significant difference. Most changes tended to be cosmetic upgrades including a new variety of colors to choose from, newly designed wheels, and woven vinyl seat inserts. The mustang received a new grille pattern, with chrome edges and horizontal inserts, which replaced the '65 honeycomb grille. Another adjustment to the grille was a modified Mustang Pony emblem that seemed to float unsupported in this new slatted grille. The grille alone is the easiest way to tell the '66 Mustang from the '65 model. A new automatic transmission option was then available for high power V-8 models. Also included was a new instrument cluster, a new rocker-panel trim, and improved the side scoops by adding chrome trim with three wind-splits. In the Mustang GT models, it was made standard they receive the new gas cap and driving lamps. All Mustangs, except the GT, received the Mustang Pony emblem behind the front wheel wells. The coupes that contained the high-performance 289 engine received a unique Hi-Po 289 emblem on the fenders.

Ford made a larger assortment of colors to accommodate the appeal and changes the new '66 Mustang would possess. The variety of colors available included: Antique Bronze, Arcadian Blue, Brittany Blue, Candy Apple Red, Dark Moss Green, Emberglo, Ivy Green Metallic, Light Beige, Maroon Metallic, Medium Palomino Metallic, Medium Silver Metallic, Nightmist Blue, Raven Black, Sahara Beige, Sauterne Gold, Signalflare Red, Silver Blue, Silver Blue Metallic, Silver Frost, Springtime Yellow, Tahoe Turquoise, Vintage Burgundy, and Wimbledon White. These many options of colors made it possible for buyers to personalize their Mustang to fit their unique styles and tastes.

Four engines were made available in these cars. The 200 cubic inch six cylinder featured one-hundred twenty horse power with 9.2:1 compression and a one-barrel carburetor. Second, the 289 cubic inch V-8 engine produced two-hundred horse power with 9.3:1 compression and a two-barrel carburetor. Third, the 289 cubic inch V-8 engine that made two-hundred twenty-five horse power with 10.0:1 compression and a four-barrel carburetor. The last, but definitely not least, was the 289 cubic inch V-8 engine that scooted away with two-hundred seventy-one horsepower with 10.5:1 compression and a four-barrel carburetor.

The original Mustang fastback was discontinued in 1966 because of a fifty-percent decrease in sales in the previous year. Only thirty-five thousand of these cars were produced.