Check power when the electric pto is on. Has to be a short somewhere.
Or power is being used for the PTO but alternator charge is not getting back to the battery. Broken ignition contacts, burnt fuse, broken ammeter, bad pto switch. These are all suggestions for testing only. I would also check all wiring for wear spots. I have no idea what is wrong with it.
With the battery fresh, it should test at about 12V. Engine idle, it should test at about 13.
5. What does it test at when the electric PTO is switched on?