This sounds like a charging system problem, but don't be too quick to blame the alternator. The voltage regulator controls system voltage and he lives inside the Engine Computer. That circuit causes very little trouble. When there is an over-charge condition it is more common to find a grounded control wire between the alternator and the computer.
To start the diagnosis, you need to monitor system voltage while the problem is occurring. You'll need to connect a digital voltmeter to something that has full battery voltage. That can be the cigarette lighter, a fuse inside the car, or a fuse under the hood. If you go under the hood, you can clip the meter under a wiper arm. You should see 12.6 volts with the engine off and the battery is fully-charged. With the engine running, the voltage must be between 13.75 and 14.75 volts. It should remain steady regardless of engine speed.
If the voltage is too high or it goes higher and higher as engine speed goes up, you'll need to measure the voltage on the smaller wire on the back of the alternator. There's two of them in a small plug on the back of the housing. The alternator is on the left side of the engine near the bottom. One of the two wires will have full battery voltage. It's the other wire we need. It will have 0.0 volts, full battery voltage, or something in between. It's the something in between, typically 4 - 11 volts, that is normal. For your symptom I'd expect to find 0.0 volts. That would point to that wire is shorted to ground. The cause of the problem could be in the alternator itself, but that would be very rare.
Friday, September 16th, 2016 AT 9:31 PM