ignition light on when idle

[Tim]

Recently the ignition light is always on when the engine is idling and the reading on the VDO voltmeter is fluctuating between 11.5 and 13v (it was stable at 13.5v before). The alternator (Brazilian made Bosch) was bought new when the engine was rebuilt 2 years ago and it's got only 3000miles now. Do I have a faulty alternator? Or is the battery going to die?

[NO_H2O]

Sounds like 1 of the diodes has given it up in the alt. DC power is made from AC power in the alt. with a retifier circut of 3 diodes. When one of the 3 goes bad you will have pulsating DC power _-_-_-_- instead of steady DC power ________. You can have an Alternator repair shop relace the bad diode or test the circut. Or replace the alt.