Here is the rear, or slip ring end, of the 12Si alternator.
Compared to the 10Si, this model has a lot more holes in the rear for better airflow. The small slits over the rectifier have been replaced with a large rectangular window. You can also see that the bridge rectifer has a larger, better designed heat sink over the small sawfin design of the 10Si. You can also see the D-shaped test hole and an M8 threaded hole for grounding and mounting. On this model, the two voltage regulator pins are visible, but there may be a black rubber cap there if the 12si alternator is self-exciting. The bearing is a high quality needle bearing. We normally use INA bearings with high-temperature grease, giving you an extremely durable alternator.
This particular model comes in many outputs and voltages. It can be upgraded to a maximum output of 140 amps with a new stator and bridge rectifier. You can also replace the voltage regulator and rotor to give you various voltage outputs, from 6V to 24V. Positive ground and negative ground rectifiers are also available if you are replacing an older generator on a tractor or antique vehicle.
This is an extremely easy to repair alternator. All of the components are fixed with screws, so you don't need any soldering skills or tools to fix, just a set of nut drivers and maybe an impact wrench to take the pulley off. You don't normally need to remove the pulley if you are just rebuilding the unit. Just take out the four thru-bolts and remove the back cover. Be sure to reload the brush holder before reassembling the unit. The voltage regulator sits directly underneath the brush holder, so if you are converting it from a 12 volt unit to a 6 volt unit you can easily reload the brush holder while it's removed from the alternator.