Brake warning light on

Centering is by creating a leak on one side and stepping on the pedal until the light goes out, as the valve shuttles over. It is best to do this right at the M/C or combination valve. This is very messy business.
Instead
One trick I have, is to clamp the rear flex hose and then crack a front bleeder. Then brake hard until the light goes out,close the bleeder and release the pedal. Don't forget to remove the rear clamp.
Alternatively to clamping the line, you can crank the rear adjusters to push the shoes out hard to the drums.
The object is the same, to prevent a place for the rear fluid to go while centering the valve.
It's usually the rear that needs to be moved.
You cannot achieve anything by removing the switch.
But before you tear your hair out, make sure the parking brake sw is not engaged. It will turn the light on too!