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Old 03-09-2013, 14:09   #1 (permalink)
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alternator light on


Can anyone help by telling me where all the earth leads are as I think I have a bad earth connection somewhere! the alternator is working but not charging the battery and the dash light is on. The last battery died so I replaced it! car starts no problem but it's not charging the battery.
Has anyone any idea what I should be looking for and doing to fix the problem?

Many thanx
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Old 06-09-2013, 11:23   #2 (permalink)
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If you have the alternator light on it is probably the alternator that is at fault. The way the warning light works is really simple as it is basically a diode. If the alternator output is greater than battery output then the diode will not pass voltage and the light stays off. If the battery voltage is greater than alternator then the diode will allow voltage to pass and the light comes on. If you have the light on then it wont be an earth but the alternator output that is at fault.

Just out of curiosity, have you removed the exhaust heat shield in the engine bay (or is it even there in the first place)? A lot of people remove them as they crack and rattle badly the only problem is that it is there to help protect the alternator and if it is missing then the effect is that the alternator gets to hot and it fails prematurely.

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Old 19-09-2013, 09:13   #3 (permalink)
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Thank you for the info. Yes the heat shield is long gone! The alternator was working before I parked the car as it has been stood for quite some time now (6 months) then the battrry died so I replaced it but as soon as I started the car the light came on I checked what earth leads I could see and all seamed fine and the alternator seems to be outputting voltage! I will double check the alternator output and recheck all leads. If that fails it looks like a new alternator! Another thing to add to the list of bits to get to put it back on the road.
Many thanx.
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Old 22-09-2013, 11:17   #4 (permalink)
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The alternator should be charging at around 14.2 volts, it is probably worth checking the connections onto the alternator
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Old 19-11-2017, 11:14   #5 (permalink)
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Help, I have the same problem with my ZR160. The Warning Light started coming on - at first intermittently, then all the time. First time I had a proper look in the engine bay I found both battery terminals rattlingly loose on the battery posts (the car had been at the Auto Electricians about a month before for electric window fix). After I fixed the terminals the light went out - for about two days. I reasoned that arcing across the loose terminals had probably done for the rectifier in the Alternator so I ordered a new one. It took two weeks to get here & today I spent most of the day fitting it (there was an issue with the connector which I'll post separately about).
Result is the light's still coming on! (it did go out briefly but soon re-lit itself). Cannot believe there's the same fault in two alternators - where else do I look?
Incidentally with the original alternator & after the light came on my stepson discovered that the car would keep running if you pulled a battery terminal off - with a voltmeter there was about 0.2V more from the Alternator than the battery on its own.
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