Roverbo Posted November 28, 2010 Share Posted November 28, 2010 A friend of mine has asked me to help with this subject. But I can´t figure it out. Any good ideas, anyone? Quote: "RRC 1991, 3.9 EFI ABS. Today my charging lamp turned on, as I was driving in the snowy conditions near Copenhagen. But the battery measures 14V when engine idling. Doesn´t that mean that it is charging? Engine idle = dimmed light in the charging lamp. Higher revs = full light. Ignition off = light off. Ignition on = light on. I checked cables and used the multimeter: Engine idle (800 revs): 14,0V on the battery Ignition turned off: 12,6V on the battery Cable from alternator to battery (+) is fine. Ground wire from battery to frame is also fine. Connection from alternator housing to battery minus is also fine. I´m confused. Does the 14V mean that the battery is charging? How come the charging lamp is lit then? Best regards, Anders Lindberg" Unqoute. Quote Link to comment Share on other sites More sharing options...
SteveRK Posted November 28, 2010 Share Posted November 28, 2010 I'm not sure of the specifics of this but I think one of the diodes in the alternator is shorting to ground, hence the ignition light coming on with the engine running and alternator is charging. If so and depending on the model of alternator you can sometimes buy the diode pack as an assembly instead of exchanging the whole alternator. Quote Link to comment Share on other sites More sharing options...
g&t Posted November 29, 2010 Share Posted November 29, 2010 I had exactly the same problem with an '89 3.5efi. At first the light would go out some of the time but in the end it glowed all the time the engine was running, at any speed. I think the prob. is caused by a failed diode connected with the battery light itself but if you are getting that voltage at the terminals it's certainly charging. Mine had the fault for over a year 'till I sold the car & the mate who bought it never had any battery problems either. Quote Link to comment Share on other sites More sharing options...
Range Rover Blues Posted November 30, 2010 Share Posted November 30, 2010 The field coil runs from one of the 3 phases via the doides. It's one common fault on old alternators and the fault might develop into a breakdown (might not) so get a spare alternator. The 1991 3.9 should be a 4-belt engine with a 65 amp alternator, they are quite cheap to rebuild and worth the cost of a new diode pack (later alternators aren't as strong). Quote Link to comment Share on other sites More sharing options...
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