The H6 charging system incorporates some ECM control of the alternator so that the alternator load on the engine can be reduced when the battery is fully charged or “full engine power” is needed. However, if the battery is low, under normal driving the alternator output should be at a charging level, i.e., above 12.7 Volts and probably closer to 14 V.
In both trouble cases posted here it appears the problem isn’t necessarily load-related. The alternators are failing on their own. It could be a problem in the internal regulator, or the brushes, or a bad contact, or bad grounds.
The H6 uses a different alternator. Both the H4 and H6 alternators have the same 3-pin connector; in the H4 only two connections are actually used, whereas in the H6 the third goes to the ECM. The two alternators are not interchangeable.
Also, there’s a number of threads here where aftermarket new or rebuilds for the H6 didn’t work or didn’t work for long. Generally the suggestion is to find a recycled original factory alternator. @eagleeye has suggested a source of new alternators in the past — see this post (in fact, that whole thread might be of interest).
