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Not an alternator problem, or is it?


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Yesterday the battery light came on on the RR and refused to go off. It's bright as normal with engine off and then about 50% when running. Battery voltage was about 11v with the engine running. So, I assumed the alt had bitten the dust and spent a delightful half hour this afternoon being rained on while I bolted my spare one in. Lo and behold, same behaviour! <_<

Now it's possible I've got a pair of duff alternators, but it seems unlikely. I would suspect the battery, but it holds charge OK and the low running voltage suggests to me that it's not actually getting any/enough juice. That leaves the wiring, but the charge light being on would seem to indicate that that bit's doing it's job OK. That leaves the main alt wire.

Can anyone think of anything I've missed before I start re-wiring? :unsure:

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Have you done a drop test on the battery? That would give you a good indication of it's general condition, although as far as I'm aware - the charge light would go out even if the battery was totally useless. Any chance you could put one of the alternators on another vehicle to see if it does the same thing. I have to admit electrics is definitely not my strong point.

Les. :)

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Get motor running and turn on headlights.

Check voltage alternator output to alternator casing.

Voltmeter from alternator casing to batt negative and then voltmeter from alternator output lug to batt positive. Both should be less than 0.5 volt.

The charge warning lamp will glow whenever there is a difference between alternator output and battery voltage.


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