18 Pa.C.S.A. §3928.  Unauthorized use of automobiles and other vehicles.

(a)  Offense defined.–A person is guilty of a misdemeanor of the second degree if he operates the automobile, airplane, motorcycle, motorboat, or other motor-propelled vehicle of another without consent of the owner.

(b)  Defense.–It is a defense to prosecution under this section that the actor reasonably believed that the owner would have consented to the operation had he known of it.