Chasing same issues again any ideas? ‘34

[34 fordor owner]

Did some voltage checking today.
From the battery: 6.4 volts
To the ignition switch: 6.4volts
Ignition switch to resistor: 4.9 volts
Resistor to coil 2.2volts
(Big drops here so still have the hot wire temporarily in place)
Battery to starter switch:6.4volts
Starter switch to starter:3.4 volts
Another drop here which would be the cause to my slow starting issue. I’m guessing I would need about 6 volts to the starter to. So what’s the best way to clean the starter switch connections, or can I even clean up these connections? To see if I can fix the issue that way?