The Hall Effect sensors we’re using come from a rally savant in Spain. One nice touch that he includes is an indicator light—on the sensor itself—which tells you it’s working.

See, there are several ways to assemble this kind of system incorrectly. (I’ve tried most of the incorrect ways…)  Once you’ve done that to yourself, and skipped the testing because “I know it’s right”, only to find yourself at the rally without a odometer, you’ll never skip the testing again.

So when you’re mounting these sensors, putting the magnets in place, aligning the barrels of the sensors to the face-plane of the magnets, adjusting the gap distance, … your testing can take place under the car. All you need do is power the Rabbit box, spin the wheel (or brake disk, in this case), and watch for the lights.