I use one of these.
SCHNEIDER ELECTRIC Prox Sensor, 8mm, NPN, NO, Rge 1.5mm, M12
Electrical > Switches > Proximity Sensors and Switches
Proximity Sensor, Cylindrical, Inductive, Dia 8 mm, Length 2.4 In, Width 0.31 In, Depth 0.31 In, Volts Type DC, Voltage Range 12-24, Circuit Type NPN, Detecting Distance 1.5 mm, Shielded, Temp Range -13 to 158 F, Max Load 50 mA, Case Nickel Plated Brass, NEMA Type 4X, Connector Type M12, Standards UL, CE, RoHS, CSA
Grainger Item # 1EVJ4
Price (ea.) $86.30
Brand SCHNEIDER ELECTRIC
It is a proximity sensor from WW Grainger. 12 VDC NPN 3 wire.
I mount it so it senses the bolts on the rear brake rotor. Works great. I use 6000 pulses per mile.
I just order the other wheel, cover and spring from the RT Splitter box. I also drill out the splitter box for the curse cable.