vss vs tach

The way I understand this is that the Tach wire is a pulse indication engine RPM and the VSS indicated the speed of the vehicle (8000 pulses per mile).
Does the tach wire pulse once per rpm or how does that work? Analog or Digital?

I have a 1997 Mercury Cougar and the chart on this site says the VSS wire is located at transmission. Surely it's accessible inside the car somewhere? I would like to build a module to lock the doors when the car gets above 15MPH or so.

~Mike

Tach wires are typically a pulsing digital signal and can pulse from anywhere from 1/2 ppr to  1/2 as many cylinders as the motor has ppr - it all depends on where the signal is grabbed from.

If you want speed controlled door locking you want the VSS signal.

The VSS location will vary from car to car - its hard to say if you can grab it inside the car without taking a first hand look.

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Kevin Pierson

Speed Sense

PURPLE

(AC)

ECU MODULE TO THE RIGHT OF GLOVE BOX PIN 14 OF A 26 PIN PLUG

You can try that location, perhaps it will be easier to access

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Life moves pretty fast; if you don't stop and look around once in a while; you could miss it.

Ok cool. That location seems to be where everything else is too.