I would check the wiring especially the connectors for corrosion and loose connector terminals,If that checks out the switch is the easiest and cheap item to try,also safety switch at the seat will need to be checked. .the pto clutch is not cheap I'd only.buy one after you have eliminated everything else, I cant suggest this for safety reasons,but if it were me I'd run a 14 guage jumper wire right to a 20 amp fuse at the battery and power it direct and see what happens ,that will eliminate the question of whether you have a good power connection.