An external gear position sensing unit for attachment to a shift control device includes a sensor housing, a first electrical contact member supported to the sensor housing, a support member rotatably supported to the sensor housing, a second electrical contact member coupled to the support member for movement therewith and for contacting the first electrical contact member, and a coupling member coupled to the support member for movement therewith and exposed to the exterior of the sensor housing. The sensor housing, the support member and the coupling member are coupled together so that the sensor housing, the support member and the coupling member can be attached to the outside surface of the shift control device. If desired, a separate adapter may be coupled to the coupling member and exposed to the exterior of the sensor housing for adapting the sensor unit to different shift control devices.