Finding the regulator

[stihlman]

no deck just tractor

If the mower has a manual blade engagement then it will be fitted with a dual circuit alternator so the kights will be AC and get brighter as the revs increase because the voltage increases.
If it has an electric clutch then it will have a regulator

 

[StarTech]

I am like you i could not find the model so I tried to get close on the tractor. The engine i have the exact IPL. see my numbers below

Those decal are bad to get damage and it does appear that the C you think it is, is in fact a zero.

As the diode in the six wire there is actually two as that harness is for a twin cylinder engine. Besides that the kill circuit and not the charging circuit.

Here is the wiring diagram for your mower.

 

[Born2Mow]

There is also a strange physical phenomena of diodes that can be used here. Most diodes will have an internal voltage drop of 1.4V when passing electrical current. If you simply buy some surplus diodes and put 1 on either battery lead, the battery will only receive 16 - 1.4 or 14.6V which is an acceptable battery charging voltage.

An AGM battery type would love that charge voltage !! A regular wet-cell battery could stand that for 4 hours.

Cheap Surplus Power Diodes Here

 

[StarTech]

Actually the forward voltage drop is about 0.85 @ 3A. for the 1N5402 diode.

 

[Born2Mow]

OK, so place multiple diodes in series. 16 - 0.85 - 0.85 = 14.3V. Perfect.