Eric,
Yes it looks like you have a stator brake system, a piece of complicates circuitry to keep the pencil dicks trying to prove Darwin was wrong happy.
The green wire is the braking system, It goes to ground which puts a massive load on the stator and stops the engine about 3 revolutions faster than it would have without it.
A simple diode system produces pulses of DC from 0 V through to a peak ( 18V in your case ) then dropping back down to 0 V followed by an equal amount of time while the diode is converting the - side of the wave to heat then back to 0 V again.
What is critical is the Volts at the battery so take your reading there.
These crude, rude & unsofisticated systems use the battery to regulate the system voltage.
If you read better than 15V at the battery then you can start to worry.
In some systems the lights must be on to soak up the excess current and in particular the - side of the cycle as the lights are just a resistance and does not care it they get AC , DC or even BC .
These are the ones where the lights come on whenever the engine is running.
As for you manual, it has been available free of charge as a digital download for eons.
GO to there web page, plug in your engine numbers and it will bring up your owners, service and parts manuals.
If it asks you to log in, click on the "guest" option.
If that does not work you can get it from this site
http://www.mymowerparts.com/about_us.php.
Click on the "free manuals" link in the red navigation bar then navigate through to the Kohler section.
The 917 of your serial number indicates Roper as the manufacturer of your machine and Roper were made by AYP a company that Husqvarna took over so you might find a service manual by trolling through Husqvarna archives.