Charging issue that is intermitiant

JIM OF TENN

MEMBER
2002 DODGE DAKOTA
160,000 MILES

When I start engine, the voltage reading often does not come up to normal but stays at about 12v for a short time and then drops to zero, turning on the check gauges light. I can quickly turn off the ingition switch and back to the run position which resets all the system. Sometimes, this brings the votage up to normal but if it does not, I repeat the ignition off-run switching and eventually the voltage comes up to normal and remains there for the duration of the run. This can take from a couple of switches up to a dozen or more. Have been told it indicates a bad regulator/alternator and also been told the ignition swithc can cause this problem. Any ideas?
Jim

1 Reply

CARADIODOC

MECHANIC
33,741 POSTS

Sounds more like a bad diode. Have the alternator load tested with a tester that shows "ripple". If the ripple is high and the maximum output is close to one third of its rated capacity, (30 amps from a 90 amp unit), one phase is dead. That's almost always from a defective diode.

Nippendenso alternators also develop worn brushes that will cause intermittent operation. To identify that you have to measure the two voltages on the two small wires on the back of the alternator while the engine is running and while the problem is occurring. One must have full battery voltage. The other one must have less but not 0 volts. If you find 0 volts on only one wire, the brushes are open. I recently replaced mine for nine bucks.