The Magnetic Proximity Sensor will respond to pulse signals across a 1/16-inch air-gap between the sensor tip and disk-rotor, IRS-CV joint bolt-heads or notched brake-drum edge. It is useful on trans-axle setups or transmissions without mechanical speedometer cable connection. Using a stock GM Speed Sensor - 700R, 4L60, etc. Our Speed Pulse Convertor Box is used on late model GM 700-R or 4L60 over-drive transmission applications with a GM VSS (Vehicle Speed Sensor). This Convertor Box will convert the signals from the stock GM-VSS so your Classic Programmable Speedometer will read and operate correctly. The original GM-VSS signal can still be used to operate your fuel-injection, engine monitoring, transmission shift points, etc.