Replace the switch.
They are crude rude & unsofisticated simple slide switches which carry heavy current so eventually burn out.
IT is held in by a couple of barbs on the short sides of the switch so you squeeze then in & push it up then disconnect the wires.
Not as easy as it sounds.
All PTO switches are wired the same so you just need to get one with the same pin layout.
Handle colour makes no difference to the switch.