Alternator light on sometimes

[madpanfan]

Hi, newbie here.

My sisters 94 Colt (4g13 I think) has the alternator light on now and again.
It only happened today. Giving it a rev doesn't always help.
The belt is good and tight, with no noise.
New-ish battery, with clean and tight connections.
Eventually while driving, the light might go out.
It was getting near 14 volts at tickover, I didn't rev it while doing the check.
127,000 miles on clock.

Hope this post is in the right place, I did try to find the correct place for it!!
Please help.
madpanfan

 

[Arnold]

Thread moved to K11 section

Good luck with your problem

 

[Demarest]

Maybe the alternator brushes are worn? try replacing them and see if there is an improvment.

 

[K10Daz]

If it is a bright light then it indicates a fault with the battery, if its a dim light it indicates a fault with the alternator.

Check fuseable links
Check Alternator cables and earths.
Check the battery has at least 70% charge (amazing how a new battery might die)


Hope this helps

Daz

 

[Ed]

If it is a bright light then it indicates a fault with the battery, if its a dim light it indicates a fault with the alternator.

No it doesnt.

That light represents one thing, which are the alternator field windings working (i.e. generating). If that light comes on, and the belt is fine then 99% of the time the alternator needs replacement/service.

 

[K10Daz]

jus going with what i was told at my training centre.

 

[Fordy]

daz do you go to emtec in nottingham?

back on topic tho

if you have 14v at the battery when its running then the alternator is charging, but it would be better to get a battery tester that tests the alternator aswell (loads on, loads off, diode checking etc)

if not you might need to check the wiring diagrams etc

 

[Ed]

jus going with what i was told at my training centre.

Ok sorry if I sounded blunt. In many cars the current that passes through the bulb when the ignition is on creates the current that starts the field windings. (an alternator of the type used in a car wont generate just by spinning it it needs the windings to be energised first) once they are working they then generate their own power. When they do this the light goes out. When things like the brushes start to wear the field windings can begin to collapse if they do the light will begin to show.

 

[K10Daz]

Its cool, Its possibly one particular system we were told about, but , if the battery charging light is bright then it "possibly" indicates a battery fault because the alt is providing the voltage to make the light illuminate and all of the other electrics, but if it is the alt at fault then the battery cant really cope with providing the electrics for the car and power the light too if you understand me. However the whole charging system should really be checked.

And fordy nah i dont go to nottingham, im up in Scotland. Get sent to GTG in sighthill and another centre elsewhere thats not long been built, a specialist renault centre.

 

[NeX]

i'm gonna sound like a proper dumbass but i didn't know there was an altinator light, isn't there just an engine light for anything to do with the engine, including the altintor??

 

[K10Daz]

The battery charging light, the little red symbol of a battery m8.

 

[madpanfan]

I had a better look and it was very black looking on the outside. Needed a quick fix so I just stuck a reconditioned unit in instead. Seems better so far.....

Now I can play with the old one :laugh:

Cheers,
madpanfan

 

[NeX]

The battery charging light, the little red symbol of a battery m8.

ARE! thanks for clearing that up i was thinking of the orange engine light :doh: