No, KITT from Knight Rider is NOT a Cylon.
Glen Larson, creator of Knight Rider, also created Battlestar Galactica, and he so liked the red sweeping light on the Cylons that he had it incorporated into KITT's design. And not only that, but you aren't the first person to think of that. On the Knight Rider Season 1 DVD set, Larson's commentary specifically mentions the red light thing to hush up you fanboys.
By the way, the voice of KARR, KITT's evil twin, was done by the same guy who did the voice of the Cylons. It was one Mister Peter Cullen, who you probably know better as the voice of Optimus Prime.