[bobcowan]

A VR sensor is a magnetic coil that responds to a metal object (like a tooth) passing through it. As the field changes, it creates a analog signal that looks like a sine wave. The ECU receives that analog signal, converts it to a digital square wave, and then amplifies it for the rest of the system to use. it has only a signal and a ground wire, and does not need power.

A hall sensor is the same as a VR, but it has an additional circuit inside that converts the analog signal to digit. It sends a square wave signal directly out of the sensor. The ECU then gets this signal, cleans it up if needed, and then amplifies it for the rest of the ECU. The additional converter circuit inside the sensor needs power, and uses the same negative ground wire. Because of that, it's not supposed to need a pull up resister - it's part of the 12v circuit.

That's what I understand in a nutshell.

Because it's a Hall sensor, there's no need for a pull up resister anywhere in the circuit. Or so I was told. The people who built the ECU and sold me the Hall sensor says it's not needed. But, more than one person on the MS forum recommended it - even a pro-builder and dealer for MS. I figured, what the heck? Give it a try. It costs <$2, and only took a few minutes to install. I really had nothing to lose. I put it in the pigtail of the sensor because that's easily accessible.

The pictures don't show it, but I covered the leads with liquid electrical tape. Bare wires and leads bother me. (Yes, I'm a little OCD)