According to the factory shop manual, the '48 Frazer standard and Manhattan, one wire on the starter button (says it's white but it likely faded to tan as most do) goes to the solenoid and the other wire (also white) goes to the switched side of the ignition switch. So with the ignition switch on, there should be 6 volts on one side (or the test light should light on one side) and the when button is pressed, the other side should light too and the starter solenoid should energize and spin the starter.