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charging indicator lamp problems


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My charging indicator lamp refuses to come on and my alternator doesn't charge the battery. I've checked and tried the following:


There is continuity in the brown and yellow wire that goes between the charge indicator lamp and the alternator's exciter circuit input terminal.


There's 12V at the heavy-duty brown leads from the alternator to the battery.


There's 12 volts (with the ignition on) at the other terminal on the charge indicator lamp.


The bulb (24 volts, 2 watt rating) in the charge indicator lamp is OK; I've swapped it round with the indicator lamp bulb.


When I measure the voltage at the brown and yellow wire with the ignition on, it starts at 12V and slowly drops to approximately 9 volts where it stabilises.


When I earth the brown and yellow wire (via a fuse) at the alternator the charge indicator lamp doesn't come on. Given there's 12 volts at one side and earth at the other side of the bulb I would have thought it would light up.


The battery is earthed to the engine block which is in turn earthed to the chassis. The connections are clean and tight.


I've tried several different alternators that I've begged, borrowed and stolen and none allow the charge indicator lamp to come on. I suppose they could all be duff but at least one used to work when it was last used 2 years ago.


The car is a 1996-spec DeDion with a Zetec engine and normally a Lucas LRA101 alternator.


Any ideas what's wrong or where I should be looking? My Bosch Automotive Electric Systems book indicates that there's a resistor in parallel to the exciter circuit which is grounded to insure that the charge indicator lamp comes on when there's a fault in the exciter circuit. Any idea where this resistor is and what its rating is?




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