When Goliath is driven out of the garage, a model is used. To conceal the fact that there is no driver, the windshield has been deliberately obscured with dirt and mud. However in all other exterior shots, the windshield is perfectly clean.
During his escape, Garth kicks a fellow inmate who tries to climb into Goliath after him. In the close up, Garthe faces the man from the front and kicks with his left leg, then we cut to a wide angle he is facing him from the back and kicking with his right.
When K.I.T.T. flat spins off of the cliff he has to deploy his parachute. As he's floating back to earth you can clearly see that it's a model car. All of K.I.T.T.s windows are painted silver instead of looking like glass.
The layout of the room that Ms. Curtis and Mr. Miles are transferred to following their escape attempt does not match the layout presented on one of K.I.T.T.'s monitors.
Towards the end, as Goliath is pulling off the dirt road onto the highway, Garthe honks the horn on the semi truck several times as he turns onto the main road. When he does this, you can see the shadows of the camera and all the crew filming the scene on the road as Goliath drives by.
When Goliath is being driven to the prison, there is not desert or dry lake bed. When it leaves the prison, it's shown driving across a dry lake bed like KITT is in the opening credits.