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Adam,

Indeed, the Probes are a resistance/capacitance circuit that yields a frequency that varies with the fuel changing the capacitance.  When the probe is hooked to the computer the red is +5v, the black is ground and the white is the square wave frequency output back to the computer.  When you claibrate your tanks, you will supply frequencies to VM and they will program the ROM that converts frequencies to gallons. How do I know this?  VM insists that the probe must be at least 14 inches long and they are right.  I installed my LNC2 header tank probe vertically from the sump to the top - a distance of about 8 or 9 inches.  When I calibrated the tank, the frequencies increased until the fuel level was reduced to about 2 gallons and then the frequencies reversed themselves -- actually, they got so high that the computer could no longer recognize them.  Using Radio Shack CMOS components (they run on 5 volts), I utilized a schmidt trigger to clean up the square wave, and another component to build a frequency divider.  Wired as a bulge in the cable that connects the probe to the computer, the new frequencies behaved quite nicely and the fuel level in my header is accurately reported from 0 to 9 gallons.

I hope this helps your understanding of the probe circuit. (And, I hope I remembered the 1996 wiring correctly).

Scott Krueger

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