An embodiment provides a wiring harness that connects a telematics device to a host vehicle. One embodiment of the wiring harness may include: 1) a cable featuring a plurality of wires; 2) a first connector featuring a snap-on adaptor that attaches to a connector core with a pin configuration that mates with a diagnostic scan tool; 3) a second connector that connects to an in-vehicle diagnostic system; and 4) a third connector that connects to the telematics device. A wiring kit embodiment and method embodiments for coupling a telematics device to a host vehicle are also disclosed.