If you don't have manuals for your machine, get the model and serial numbers of your machine and go to the Scag website and download the manuals for your specific machine by serial number. In the parts section are the wiring diagrams. I print the wiring diagrams and then blow them up on my printer so I can read them.
Remove the fuses or disconnect the battery and do continuity checks progressively on each section of the PTO electrical system from a good starting point to the clutch. PTO switches and their connectors are possible trouble spots. Any connector can be a trouble spot. Your clutch may be either a Warner or and Ogura make, their websites have clutch info. Scag has a control module incorporated into the electrical systems which replaced the relays that were used on older machines. The control module makes trouble shooting the electrical system more difficult than when relays were used and it is a big dollar item!
Mad Mackie in CT:biggrin::laughing: