Well....On my 49 the switch is part of a cable that connects to the wiper motor.
I can't imagine it is much different on your 48.
To remove the wiper motor you would take the switch out too as it's easier to then remove the cable.
My parts book says: code 23-67-188 CONTROL, Windshield Wiper 1941-48 All with Vacuum Wipers P/N 898-522
That should get you close. The code will tell you what section (23) of the parts book to look and the location.