Ignition lamp and charging query
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Hi I have been for a drive today of about 25 miles being a hot day I wanted to see how the new cooling system worked. All well there but 
When I got home I noticed the ignition lamp glowing very slightly at higher revs , then when I measured the voltage I found 12.36 V at the battery with the engine running but 12.6 v when switched off. Lastly the ignition lamp is not illuminating when the engine is not running but does come on briefly when you switch off.
its probably obvious to a few who know but that's not me. Oh and the alternator felt really hot which I have not noticed before. Like lots of parts its not done many miles but is around 4 or 5 years old.
any ideas ?
thanks Steve

When I got home I noticed the ignition lamp glowing very slightly at higher revs , then when I measured the voltage I found 12.36 V at the battery with the engine running but 12.6 v when switched off. Lastly the ignition lamp is not illuminating when the engine is not running but does come on briefly when you switch off.
its probably obvious to a few who know but that's not me. Oh and the alternator felt really hot which I have not noticed before. Like lots of parts its not done many miles but is around 4 or 5 years old.
any ideas ?
thanks Steve
- Concrete-crusher
- Third Gear
- Posts: 389
- Joined: 09 Jun 2013
- Location: UK
Alternator diode failure, disconnect the battery before it discharges.
If you get a spark or a drop in terminal voltage when you momentarily reconnect the battery (ignition & courtesy lights off) it will confirm the above suggestion.
If you get a spark or a drop in terminal voltage when you momentarily reconnect the battery (ignition & courtesy lights off) it will confirm the above suggestion.
- Chancer
- Coveted Fifth Gear
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- Joined: 20 Mar 2012
- Location: Northern France/ Sussex UK
Yes. If you've got an alternator you should be getting nearer 14v when running.
Should repair - DIY kit for <?15 if happy with bearings (?7 more) but replacements are pretty cheap and readily available.
Should repair - DIY kit for <?15 if happy with bearings (?7 more) but replacements are pretty cheap and readily available.
- MarkDa
- Coveted Fifth Gear
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- Joined: 15 Apr 2017
- Location: Stroud
I fitted new diodes when this happened on a fairly new (Ebay) alternator.
It went again after a hundred miles so I bought a new alternator for ?35 from a reputable parts factor and its been fine ever since.
In my opinion just buy a new unit, it's not worth the hassle and uncertainty fitting a new diode pack
It went again after a hundred miles so I bought a new alternator for ?35 from a reputable parts factor and its been fine ever since.
In my opinion just buy a new unit, it's not worth the hassle and uncertainty fitting a new diode pack
- jono
- Coveted Fifth Gear
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- Joined: 17 May 2007
- Location: The wet bit in the top corner of England
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