Electric pto won't disengage, gravely 1548 walkbehind

Could be your switch is bad .unhook switch and see if it goes off
Luck

I replaced switch,could a wire be shorted,I take belt off to start then put it back on to use but its kind of dangerous.

Could be a inline diode bad causing power to be there all the time,
Check your relays this is the most common problem.
Luck