AFAIK the only discreet components inside are diodes, coils, and the regulator. I had mine apart recently and didn't see a resistor inside.
Should be testable on the bench though by connecting I, S, and the main stud to a 12v battery, negative to the case, then spinning the alternator to 2000rpm and checking for about 14.4v on the battery.
How many miles has your 90 done? Just did brushes on mine in its second alternator. Car has done 382,600km