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Glowing Alternator Light

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#1 CMA


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Posted 04 August 2011 - 02:54 PM

On the way home from the meet last night I noticed there was a very slight glow to the alternator light. Its such a tiny glow you wouldn't see it at any another time apart from at night so I've no idea how long it has been glowing for.

Any ideas what might cause this and where I should look before I strip all the electrics down again to find out?

NB: New alternater fitted in the last 6 months and new battery fitted in the last 12 months

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#2 Longboarder


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Posted 04 August 2011 - 04:36 PM

Glow means small voltage differential between battery and alternator output. Can be low volts from alternator due to worn brushes or slip rings or diode problems or high volts from alternator due to dying voltage regulator. Glow at idle that brightens at higher revs but dims if you put the headlights on is often voltage regulator. Glow at idle that dims with revs but brightens if you put the lights on is often low alt output. Put a voltmeter across the battery terminals and rev the engine. If it climbs to 15 volts or more (often 17-18) I'd say regulator.
Or a wiring fault, short in the ignition light circuit.

Thought for the week.
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#3 CMA


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Posted 04 August 2011 - 05:06 PM

Cheers Nigel,

Glow stays the same no matter what the revs.

Will get the multi out in a while and test the voltage.


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#4 CMA


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Posted 04 August 2011 - 06:10 PM

Just tested and the Volts stay at 13v-13.3v no matter what the revs, put headlights and fan and foglight on and it stayed up at 13.2v

So to me this mean the alt is working and its probably something else causing the bulb to glow very slightly? Just no idea what.

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#5 Mark B

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Posted 04 August 2011 - 06:56 PM

13.3 with non load equals, on its way out or water in it, 14 ish is a more realistic non load figure, if the light glows it means one of 2 things,

1) a short/ water ingress

2) the alternater is not fully switching to live output.

#6 Grizzly


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Posted 04 August 2011 - 08:31 PM

I had something like this a couple of years back.
Only noticed a faint glow at night and seemed to get a bit brighter if you put more load on (ie as well as the headlights, which were on anyway, turned on the heater fan and it got brighter).
Turned out that the three connections onto the back of the alternator were a bit lose. Squeezed them all up a bit to make them connect better and the dim light went away.
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#7 DanE


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Posted 04 August 2011 - 09:04 PM

I had same as grizzly the contacts were dirty on the alt plug cleaned then tightend them and problem went
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#8 tazzzzman1


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Posted 04 August 2011 - 09:42 PM


Remember what happened to me last Oct....?
I had been getting the dreaded glowing light (only visible at night). Eventually Altenator totally packed in. Knackered brush's and voltage regulator on mine...
Might also be worth checking belt ain't slipping :rolleyes:
Are we there yet!!
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Cheers Terry