Every time KITT drives into the mobile headquarters we can clearly see that the car just barely fits, with only a few inches clearance from each side, yet Michael is able to swing the door open and get out.
In almost every episode the landscape seen through the car-windows when Michael is talking to KITT while cruising doesn't match the exterior views of KITT driving along.
Crew or equipment visible
KITT is supposed to have an air-plane style steering wheel. However, in many episodes, the top portion of the stunt-car's normal, round steering wheel is visible through car's windows.
The copyright date at the end of the credits on the first (pilot) episode shows the roman numerals MCMLXXVII (1977) instead of MCMLXXXII (1982). Some people have suggested that this may have been when the idea was conceived rather than produced.
Throughout the series, K.I.T.T.'s cameras take pictures from outside the possible viewing angle of any camera that can be mounted on K.I.T.T.
Whenever K.I.T.T. taps into electronics, the same electronic circuit board is shown irregardless of what type of electronic device it is.
Incorrectly regarded as goofs
During the entire series, "turbo boost" is used both for high-speed chases as well as for jumping. "Turbo boost" is supposed to be used for both according to the series canon.
In many episodes, David Hasselhoff's stunt double looks absolutely nothing like him and is on screen long enough to be obvious.
In many episodes, the cars used in crashes or in scenes where a car is falling in a lake are clearly model-cars "driving" through miniature landscapes.
The "tires screeching on pavement" sound effect is often added while KITT is peeling out on sand or rounding a corner on sand/gravel/grass. Screeching sounds would certainly not be heard while driving on such surfaces.