An illustrative electrical harness for bypassing a vehicular security module includes first, second, and third connectors, and electrical conductors. The electrical conductors electrically couple a first pin of the first connector to a third pin of the third connector, a second pin of the first connector to an eleventh pin of the third connector, a first pin of the second connector to a fourteenth pin of the third connector, and a second pin of the second connector to a sixth pin of the third connector. When the first connector is mated with a connector of a first communication bus of a vehicle and the second connector is mated with a connector of a second communication bus of the vehicle, the third connector is configured to bypass the vehicular security module by providing access to a diagnostic port of electrical modules coupled to the first or second communication buses.