I have an older Scag mower (SSZ 22CV 61") that came with our new house in 2016. iBased on the serial numbers, I beleve it was built in 1996.

I've been having issues with it starting ever since we moved in. I'd sometimes turn the key and get nothing but a click or clunk. I've replaced the starter and battery and each seemed to help for a time. I'm thinking the battery isn't charging.

After mowing most of my 1.4 acres, I had to stop for a bit and when I returned the battery lacked enough power to crank he engine. I only got a clunk when I turned the key. I put it on a battery charger for a short time and was able to start it.

First, I'm not exactly sure what my ammeter should be reading. It typically reads zero and goes negative (about -10) when cranking the starter. Is that what it should say?

Second, after I was done mowing I checked the battery voltage. It read 12.0v with the mower off and was 11.93v with it on and at full throttle.

Third, the rectifier/regulator has an ground wire that looks added on. It runs from the body of the rectifier / regulator to one of the mounting bolts for the engine shroud. The shroud is plastic, so the only ground that wire is getting is through the screw, which doesn't seem good. Is this ground wire needed?

So, it seems my battery isn't getting a charge, how do I diagnose it?

 

Your battery voltage should be over 13 when running full throttle. Based ont he jumper wire to ground the rectifier, it sounds like you have a Kohler command engine. That wire is necessary and the unit will not charge without it. With the engine running, test for AC voltage from each of the two outside legs of the connector going to the rectifier. If you have several volts on each, then plug in the rectifier and check voltage on the center terminal in DC mode. It should be over 13. If not, the rectifier is bad. If you don't, then there is a good chance the magnets on the inside of the flywheel have come unglued and are stuck to the stator instead of the flywheel.

 

Do a Google search for your model Kohler Engine ,lots of info out there on charging circuits.
Geo

 

Turned out to be rather simple. Embarrassingly simple.

The rectifier was unplugged. Plugged it in and all was good, 14 volts at the battery and positive 10 amps on the ammeter. After running it a while, the ammeter had dropped back to zero.

I must have unplugged it at some point, though I don't remember doing so. I had to take it apart at the start of the season to deal with a mouse nest under the engine cover, perhaps I never plugged it back in.

 

Great! Always nice when it's a simple fix.