What is Tach?

tachometer the gauge that tells you the RPM of the engine, google up tach or tachometer

Tach is in refrence to tachometer as said above. It works exactly like an electrical generator, just on a much smaller scale. As the distributor in a given vehicle spins, electricity is created(AC), just like when the shaft of a generator is driven, a field coil surrounding the magnetic shaft creates electricity. Most remote starters use a tach signal to tell when the engine is running. If no AC is detected, it could/would continue to crank the engine until some sort of AC voltage is detected, then stop cranking. Im assuming cruise controls work the same way. You press a button or flip a switch which tells the unit to keep this voltage the same, which in turn, operates the gas pedal and keeps the engine speed the same and likely keeps the vehicle moving the same speed.

I could be totally wrong about the cruise controll aspect of this. Good luck though. .