The SIR coil assembly contains 4 circuits used by the steering wheel controls. This allows voltage to be applied by the steering wheel switches to the radio while the steering wheel is being turned.

The following are controlled by the radio control switch:

The radio control switch receives power through CKT 843. When the switch is pressed to the desired function, a network of resistors in series allows a different voltage output through CKT 1796 to the radio for each switch pressed.