Started the bus today and it started and run fine, checked charging voltage and it was 14.1v, let it run for 10 mins and stopped it, took keys out and generator light is still on, disconnected i think df connection( thin green wire to dash) and light went out. With wire connected checked voltage from df connection to earth and reading 13.8v. When turning ignition on oil light comes on and genny light goes out, but starts ok. I have been having a problem with battery flattening after 4 or 5 days, but never had this light on problem before, new Alternator was fitted last winter and i think it runs a bit hot..........is it goosed? May also add with battery earth lead disconnected light is still staying on.
there should be an ignition live (black wire) in the back of the instrument cluster When ignition is on, but engine is not running there is a potential difference across the bulb (difference in voltage) which allows current to flow and your bulb lights up when your engine is running, the alternator/generator feeds 12V back to the bulb, so in effect you have 12V each side of the bulb = no current flow and light goes out. from your symptoms of the light on with keys out, I'm suspecting you may have a permanent live on the back of your instruments rather than ignition live (although that would mean the oil light should also be on with keys out), or perhaps your regulator has broken down and 12V from your battery is feeding back and finding an earth up at the cab end
I've got this horrible feeling that it is the latter Diddy, purely from the fact that i've got 12v on that terminal to earth with the battery neg lead disconnected!
as the neg is disconnected and the light is still on it suggests you have a voltage on one side ....but less of a voltage on the other, so current will still flow and the light will be on it is a curious fault I'm sure there is a 'how to' on the ignition light ....I'll have a look
here you go http://www.thelatebay.com/index.php?threads/charge-light-how-it-works-and-how-to-test.1960/ http://www.thelatebay.com/index.php?threads/bench-test-a-alternator.19813/
An alternator diode pack failure can also cause these symptoms, though the light should go out if you disconnect the battery negative. Electricity must flow in a complete circuit. If you disconnect the vehicle battery negative and the light stays on, then power is coming from elsewhere. Do you have a split charge system for a leisure battery, or solar, etc?
