I have never seen a knob on the turn signal arm in a U.S. car. Does it look like a factory setup? I have/had what 805moparkid says. My '65 Newport has an electric spray pump, with the switch a push-in on the wiper knob. My '69 Dart (stolen) had a rubber foot pump (non-electric). My '65 Dart has neither, but an after-market setup with an ugly button I removed. I can live fine without a windshield spray.