Kubota make Operators manuals, parts manuals and workshop/service manuals. They are all OEM products and designed for your machine. There are other companies that sell aftermarket manuals.
Generally wiring diagrams are found in the workshop manuals, however sometimes they are in the operators manual.
I'm guessing that you may be chasing a manual for an L175, you don't actually say, but I glean that info from your screen name?
There is an L175 workshop manual available for download from the following link, I haven't checked to see if it has a wiring diagram in it.
http://www.kubotabooks.com/AutoIndex/index.php?dir=Tractor%20Owners%20Manuals/
Instead of chasing a parts manual, updated parts listings are possibly available here
http://www.kubota.com/part/partsList.aspx