Hi guys,

My little Uno developed a prob this week. The other day as I was driving along, the battery warning light came on - something that I have never seen on before at all!
Anyways, I knew that my battery is a bit duff, so I thought its probably the battery at fault.
Anyways, I wanted to check it was not the alternator, so I did a voltage read across the terminals - about 14V when engine running, and about 13.5 under load.
So with this in mind, I concluded it must be the battery - makes sense I think.
So I went to CAFCO and bought a new battery for £30.
Just fitted it, and the car fires up quite nicely, but the battery warning light is still on.
Whether this is because I've only just fitted the battery, I'm not sure.
The other confusing thing is that the battery light comes on when I engage the ignition - so me thinks that if it was a problem with the alternator then it wouldn't know until the engine is running as obviously the alternator is not working when the engine is not on.
As an aside, the battery light has never illuminated before - the AA man told me that it really ought to come on when you put the key in, but I did just wonder if the Uno did not do that for some reason.
Also, the light does dim when the engine is running, but again I think that is just an Uno "feature".
So any ideas peeps?
I'm looking to change my car anyhow in about 2 months, so do you guys think I should be ok? I'm going to keep the old battery just in case this new one does go flat.

Thanks in advance,

Marko

check the cables going to the alternator for good connections and no breaks

custard boy said:

check the cables going to the alternator for good connections and no breaks

Click to expand...

Could it be a faulty connection to the alternator which is used for testing its working?
How does the car establish whether the alternator is working anyhow?
And should that battery warning light be coming on every time I put in the key, just like the oil pressure warning light does?

Regards,

Marko

Hi Marko,

I’m not sure why the battery light has just started working. Looks like Alex has seen a similar glowing problem before. - https://www.fiatforum.com/showthread.php?t=18879

Also in that thread, All 3 of my Uno’s normally had the battery light working with the key turned 1 click (as the AA man suggests).

I'd keep the other battery handy just in case the alternator is on its way out.

Good Luck with finding another Uno

Regards,
Louie.

The battery light should come on with the key in the "ON" position without the engine running. This is a test for the lamp in the dash, so you know it works ok. When the engine starts the lamp should go off if everythign is ok. I have not found ANY car that does not do this.

Did you get 13.5V with the lights and fan etc on? If the lamp is dim when you are driving the car that is a usual sign of a blown diode in the regulator. Either way its in the alternator and needs to be repaired.

Check all your fuses though.

Thanks for all the help guys - sounds like the problem may not be too serious then!
Steve - you said it may be a blown diode - is this serious? What will be the result of this?
It seems odd that the light never even came on before as a test when putting the key in - and it staying dim when driving - does this make it sound like its just a random issue with the instrument cluster?

Thanks again,

Marko

It means it might need a new diode, or complete regulator. this is not major. It could be a random problme with the alternator/regulator geeping the lamp on.

Is the alternator still working and charging the battery? It sounds like it so It might also be just a wiring fault to the lamp itself. I would remove the alternator and get it tested, or take the car to an auto electrition

As Steve and Louie say, the warning light is supposed to come on with the key. When this doesn't happen, I've found that it's usually the thin wire that connects to the back of the alternator with a push-on spade terminal. Often it's just hanging free, or the wire has broken inside the crimped-on terminal. It would be worth checking that first in my opinion...

The small current that flows through the warning light (when the key is on, but engine not running) serves another important function. It excites the field windings in the alternator - basically, sets up the magnetic field so that the alternator begins to charge immediately when the engine is running.

Then, the voltage on that wire matches (or exceeds) the battery voltage from the warning light, and so the warning light (which now has 12+ volts on both sides) goes out.

Otherwise, if the alternator voltage does not match or exceed the battery voltage, the light stays on (perhaps dimly). This warns you of a faulty alternator - not usually a faulty battery, since the alternator usually matches or exceeds the output of a faulty (low-voltage) battery.

If the light never comes on in the first place (without engine running), it's hard to draw any conclusions about it glowing, because you don't know whether the alternator is self-exciting or whether there is low voltage and a faulty diode etc. as Steve says. So, I think you should get the light working normally first, and take it from there.

By 'self-exciting' I mean that the alternator will probably not begin to charge until the engine hits 3000RPM+ and the fields are set up by induced currents. Without the warning light, it's difficult to know if this is happening, although your voltage measurement of 14V suggests that it was charging (perhaps only on that occasion though!)

I have seen the case where, once the light was working, normal operation resumed with no more flat batteries.

Oh and don't throw away the old battery just yet - charge it every couple of months and keep it as a spare, maybe for your next Uno as Louie suggests

Just my two cents...

Thanks,
-Alex

Just found out that a member of a local forum has been driving his Uno for 3 months with the battery light on without ever ending with a flat battery...
I do not want to make any panic here, but I measured the voltage just today (winter is coming plus it is a legal requirement here to drive with lights on from the date when the light-saving time is implemented) and it was 14,5 V under full load.
I only saw the battery light on when the alternator brushes were worn useless. I believe you cannot do wrong with checking them. If I remember right, they were funnily cheap (about 1,2 Euro for a pair) and they can be soldered in no time. It may also be they are just sticking in their guides, in which case WD40 comes handy.
Speaking of regulator...
My understanding is that it is nothing but a handful of diodes. These are dirty deeds done dirt cheap (quoting a "retro" band while speaking of a "retro" car ) when bought from an electronics parts supplier - say, 1 Euro for a dozen, but the regulator sold as a spare part is about 30 - 40 Euro.
Maybe one should try to bodger the part...?

OK guys, heres an update on the situation...

The light is still coming on, although sometimes when going down the motorway in the mornings the light does go out, only to come on later when I'm crawling through traffic in town.

As for this small cable on the back of the alternator - what exactly does it do? If it is not connected will the light come on? Or does it stay on if it is not connected?

Either ways, the battery still seems fine, so I'm not sure what the problem is. Effectively, it seems as though the light is coming on, but there is no problem.

Any ideas guys?

Well...
The small wire connects to the normal-sized spade terminal on the back of the alternator. If this wire is not connected, the light would not come on when you turn on the key (before starting the engine). Also, I don't see how the light would ever come on - unless perhaps the wire was brushing against a metallic part with the engine running! That would earth it and cause the light to glow, even though there is nothing wrong with the alternator.

Meanwhile, some alternators have the large wire fastened with a 10mm nut; others have the large wire connected through a large spade terminal. Just so you know... either way, make sure that main connection is clean.

As I wrote somewhere before, I once had a dimly-glowing no-charge light which went away when I changed the instrument cluster. You might like to try another instrument cluster, since swapping it is an easy job.

Failing that, a constant-brightness light fault possibly lies in the regulator which is attached to the brush holder for most alternators. It's simple to change this - the alternator doesn't have to come off the engine - you just unbolt the black plastic cover and then undo two 8mm nuts to remove the brush holder. Unfortunately the part is rather expensive to buy new, so it's probably best to find a second-hand one from an alternator that looks the same as yours. The brushes should both stick out by about 5mm minimum.

Hearing about the light going out at motorway speeds but coming on in town does make me suspicious about how well the alternator is working, though. Note also: if the brightness of the light seems to be varying, I think it is most likely to be an alternator fault. Fortunately, worn brushes account for most alternator problems, so perhaps by removing the brush holder you will discover worn brushes, which will account for the problem. But it could even be just a slipping belt.

As you can see, there are numerous causes - so, we need to start from the beginning, again. Get that light to come on with the key - I presume it still doesn't? - which means fixing the small wire connection. Then, test the voltage at the battery with the engine running. Should be 13.5 volts, maybe more. Listen for belt squealing - check the surface of the belt - should not be glazed or shiny and should have no cracks. Fit a new belt if in doubt. (If voltage still low, skip ahead to brush replacement...)

If the light is still staying on with constant brightness, swap the instrument cluster temporarily (doesn't even have to be the same model of instrument cluster, though has to be Mk1 if you have a Mk1, Mk2 if you have a Mk2...) and if still varying in brightness, replace the brush holder/regulator with second-hand spare.

If still no joy, change the alternator...

Good luck!
-Alex

common problem. either alternator wire connection or proberly the instrument connector.the instrument connector has a tendency to work loose and cause this sympton.easy fix.to check the wiring,do a contiunity check along the wire.