The vehicle died while being driven. The charge light had come on some time before. I tested the voltage output of the system at the battery. At idle with a discharged battery, engine running I read 12.5V, at speed the voltage topped at 13.4. I assumed the voltage regulator was working because it limited. The voltage seems low. I took the alternator to be tested and it showed that the alternator put out too much voltage something like 15.75 and the limit was 15.5V. I'm not sure I trust the operator of the machine as he had to try several times to move the ground just to get the test to run. 220,000 miles....any other simple tests....For $8 and some bruised knuckles I can change the brushes and re-establish connections to make sure corrosion is not the issue. Any other thoughts. Thanks.
Alternator testing on 2001 Toyota Sequoia
by jpollock in Peoria, AZ on December 13, 2009
ANSWER by Valleyautotech , December 16, 2009
The alternator can have a intermittent charging problem and will test fine and then hit a bump in the road and suddenly stop charging, but changing the brushes could solve this