I have a friend who is deaf too, but he is not so rude as to play noise for everyone else to hear. What you're describing is typical of a failed diode inside the generator. When one of the six fails, you will lose exactly two thirds of the generator's capacity. 30 amps from the common 90 amps generator is not sufficient to run the entire electrical system under all conditions. The battery will have to make up the difference until it slowly runs down. When system voltage gets low, computers start to do weird things. Some will shut down and some will start turning warning lights on, especially air bag and anti-lock brake computers that require a lot of current to run their systems.
You can start the diagnosis yourself by measuring the battery voltage with the engine running. It must be between 13.75 and 14.75 volts. If it is low, suspect the generator. If it is okay, the second half of the test requires a professional load tester. Your mechanic will check the maximum output current the generator can develop, and "ripple" voltage. If the maximum current is one third of what it should be, ripple voltage will be very high. It's not practical or cost-effective to replace the diodes. When one has failed, replace the generator.
Monday, February 17th, 2014 AT 5:22 PM