PTO will not engage

[Fontainerm]

my SA221 PTO will not engage. I checked the switch and wiring on got seem to be fine voltage readings. PTO has been working fine up until 2 days ago. Any ideas on what/where to check for a problem?

 

[MutantGenepool]

Is the alternator charging? Low battery voltage will not allow the PTO to engage. Check hyd oil level.