I need a wiring schematic for an S1642 Scotts Lawn Tractor.

Hi,
Schematics are only available by purchasing the service manual. Pictures of the two wiring harnesses are available at JDParts at:
John Deere - Parts Catalog
And entering S1642 will yield your model. Choose the Sectional index and know if your serial number is above or below 35000.
Peace,
Clarke