The reason why an electric starter of a riding mower ( WheelHorse and others) will not engage are:[br]
A - cranking mechanic is stuck / pignon spring if existing broken[br]
As the starter is normally a standard permanent magnet DC motor with carbon brushes:[br]
B - carbon brushes (CB) worn/stuck[br]
C- permanent magnet loose / broken
Prior disassembling the starter to check for B or C mark the relative position of its parts and remove just the non-drive side cover with the CB holders for inspection.
If the magnet is loose/broken mark the visible side, so you can reassemble correctly after cleaning (remove old glue) and reglueing (I used Loctite 548)
Try first to reassemble without glue and prepare two spacerbars to put in between the two magnets to keep them at equidistance, as well as a disk to give you the correct axial position of the magnet. The broken magnet parts have a huge force and tend to missalign as long as the new glue has not cured.
To reengage the CBcover, keep each CB inside its guide with a bended to fit wire/sheetmetal C clamp that you will remove once you positioned the collector between the CBs during reassembly.