When you insert key into ignition switch and turn it to the left you are turning on the ACC circuit. It will allow you to operate lights ,horn and other accesories, but it does not turn on fuel pump and other engine controls. It saves battery power for when you need to operate vehicle components without engine being on.
The ACC wire offers power/electricity only when you insert key into ignition switch and turn it to the left
The ACC wire needs to be connected to igniton