This page is about Variable Reluctance sensor (VR) polarity Pretty much any VR sensor can be used that came from an automobile. Ford, GM, and basically all manufacturers applied millions of them. VR sensor is a passive component, which means it does not require supply voltage. Resistance is However there are some restrictions for the wheel and polarity must be correct to be usable as the input trigger signal. The stock opel wheel is "missing tooth" ( not missing gap). Picture of the stock opel wheel: 
. [Picture of stock VAG 60-2 missing tooth wheel] Good polarity: if you measure positive voltage (DVM, DC 200mV mode, relative to GND) when approaching a ferromagnetic object (like a wrench) to the sensor. (and negative voltage when moving away). -- Missing gap Good polarity for missing gap: if you measure negative voltage (DVM, DC 200mV mode, relative to GND) when approaching a ferromagnetic object (like a wrench) to the sensor. (and positive voltage when moving away). Naive wheel When the depth of the missing tooth (/gap) is same as other teeth (/gaps). This means that the flux will not be same (because of "neighbor" effect) and the amplitude of the pulses will vary. To use a naive wheel with a v3.2 or earlier, a series resistor might be required in series with c38. v3.3 already has it for more tolerance on tooth amplitude within a cycle (eg. high amplitude peak right after the missing tooth; or accentric wheel). -- If the VR is connected in reverse polatirity it will be * 33 1.5 1.5 pattern * instead of the correct 34 2 That is a problem, since the usual practice is applied to trigger on tooth-times [...]
![[Picture of stock VAG 60-2 missing tooth wheel]](http://www.home.no/mk1classic/VEMS/Crank_60-2-wheel.JPG){kind=link}