I haven't done it with a Yanmar stock alternator
so do not know how difficult it is to make the modification necessary to connect a wire to the proper brush. This was a very easy job on our Volvo
The Sterling works as advertised once the modification is made to the alternator. The only problem in practice is that the Sterling drives these small alternators very hard. They put out their maximum amperage for long periods of time and the temperature of the alternator can reach 250°F easily.
Sterling supplies an alternator temperature sensor, which must be used if you value your alternator. Unfortunately, the alternator reaches the high temps quickly and the Sterling shuts down the current
until it cools down. So you enter this mode where it pumps high current
for 15min, then shuts down for 15min, then pumps current again, etc. It would be much better if the regulator ran at half current instead of shutting down completely.