How Remote Starter Works - How Car Starts With Remote

This is a bit technical but it can be understood like this..when we press the start button of the remote it sends a signal(Radio frequency )to vehicle.It sends (+) Positive12volts to the Ignition #1 and #2
wires (if required) on this vehicle and the Ignition turns “ON”.At same time it also sends a signal to accessory wires at the ignition switch harness that turn it "on"

After it signal is send to Starter/cranking wire at the ignition switch harness in the vehicle, spinning the starter motor over, the engine starts.

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http://www.bulldogsecurity.com/bdnew/newsite/pictures/pdfs/UNDERSTANDING%20THE%20WORKINGS%20OF%20A%20REMOTE%20STARTER.pdf