Installation of all Monit rally computers requires a speed sensor. The following options are compatible with all Monit computers.Inductive Wheel Probe - For vehicles which do not have a suitable factory speed sensor this probe is typically used to sense the bolts which attach a brake disc or propshaft / driveshaft bolts. The probe diameter is 12mm and the sensing distance is 2-3mm. Supplied with 2m long cable.Electronic Interface - Suitable for vehicles with a factory fitted electronic speed sensor (analogue or digital). Supplied with 1m long cable.ABS Sensor Interface - For vehicles with a two wire ABS wheel speed sensor. Must only be used if the sensor is no longer being used by the braking system. Supplied with 2m long cableA wiring extension kit is also available for speed sensors and comes with both 1m and 2m long extension cables. Inductive Wheel Probe Installation InstructionsElectronic Interface Installation InstructionsABS Sensor Interface Installation Instructions