The silver plate on the Horn Button Retainer (the part in your picture) makes contact with the Contact Spring and Bushing which goes thru the hub of the wheel and makes contact with the Upper Steering Column Bearing providing 360 degree continuity thru the steering wheel even when turning. The black part of the Horn Button Retainer is held in place by the nut holding the wheel on and provides the ground. The insulators (3) on the Horn Button Retainer keep the two plates from contacting while the button is at rest. Once you depress the Horn Button, the black and silver contact one another and provide the path to ground.
You should be able to sound the horn by taking a wire, stripped on both ends, holding one end to the steering shaft and the other end to the Contact Spring and Bushing.
Last edited by Phak1; 01/06/2020 2:34 AM.