This box converts your cable speedometer to GPS. Needed when switching to any transmission that does not have a cable speedometer output or you you just prefer to have a speedometer that is unaffected by tire size or gear ratio changes. Link to Purchase- www.grannasracing.com/products/speedhut-speedbox-vss-gps-to-cable-drive-converter-a-304?_pos=1&_sid=97cc66023&_ss=r