I do not know is this Elgin is OEM or Aftermarket.

It is made by Stewart Warner.. labeled as such in a couple locations.

I found reference to a John Deere Street Sweeper on Internet.... but please verify.

          1985 ELGIN PELICAN TYPE S STREET SWEEPER WITH JOHN DEERE 4239 DIESEL ENGINE

NOS Physical Condition.   

Speedometer & Odometer tested functional using an electric drill.  

Fuel & Water Temp tested functional.  

Oil and Voltmeter did not respond - non-functional.

Thanks for looking and Good Luck, Pete