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Battery light dimly lit all the time


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I am sure this has been mentioned before but as battery+light+dim in the search gave me 5+ topics from every day since the forum was started it's not practical to use the search.

The problem is, last night I was driving the 90 and noticed the battery light was lit, but it was very dim. It is usually on when the ignition is, then goes out when the car is started. It now stays on, dimly lit. I didn't have masses of electrical stuff on, only lights and cd player. The light momentarily flickered when going over a bump but this was probably pure chance as it wasn't effected by any others.

My guess is the battery is failing, it's of an unknown age and condition so I'm taking it to get tested, then I'll be looking for a new one if it's failed. What I'm hoping it isn't is an earth fault or alternator problem, so I'm interested in what people think.

Cheers

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Possibly a fault with the alternator brushes / regulator. My 300Tdi had the same symptoms - worn brushes. Worth checking the output voltage.

The brushes and regulator come as an assembly and are an easy fix. Disconnect battery, remove warning light wire from the regulator assembly, undo nuts (5.5mm AF) holding it to body and extract. Reassembly is the reverse. There's a thread somewhere in the Tech Archive covering this.

You could try the Luddite method of diagnosis and give the back end of the alternator body a tap with a hammer. If the fault goes away or the output voltage increases, suspect worn brushes.

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I'd agree with the guys above, but....

I had the same problem with mine after periods of offroading, and wading. I got the hose pipe out when i got home and washed the dirt out out. This cured the problem and it's been fine ever since!!

Bit random but worth a go!!!

Cheers

Neil

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I have seen a few doing this - it is usually a problem with the alternator but if it has the new Td5 type dash, the warning lights are a bit too sensitive and can glow dimly when there is not really a problem! Check the output voltage and also that there is no drain from the battery with everything switched off (which also points to a dud alternator)

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I am sure this has been mentioned before but as battery+light+dim in the search gave me 5+ topics from every day since the forum was started it's not practical to use the search.

The problem is, last night I was driving the 90 and noticed the battery light was lit, but it was very dim. It is usually on when the ignition is, then goes out when the car is started. It now stays on, dimly lit. I didn't have masses of electrical stuff on, only lights and cd player. The light momentarily flickered when going over a bump but this was probably pure chance as it wasn't effected by any others.

My guess is the battery is failing, it's of an unknown age and condition so I'm taking it to get tested, then I'll be looking for a new one if it's failed. What I'm hoping it isn't is an earth fault or alternator problem, so I'm interested in what people think.

Cheers

A dim battery light does not usually indicate a fault with the battery.

The battery light - or charge warning light - lights up whenever there is a difference in electical potential between the D+ output on the alternator and the positive terminal on the battery..

It could indicate worn brushes, a faulty diode or a faulty regulator.

Make sure that the cable connected to D+ on the alternator is secured correcly.

Make sure that the cable running from D+ to battery warning light and further to positive terminal on battery is free from defects. (continuity and short-circuts)

Measure the voltage over the battey with the engine off and everything electical switched off.

Measure the voltage over the battery with the engine running at 1500rpm.

These two test should tell a bit more; although it is rather difficult to diagnose which exact part of the alternator which is faulty without dissassembeling the alternator.

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Thanks for the replies so far, I've had a look today and the light is now out, though obviously as nothing has changed this doesn't mean the problem has gone away. If it makes any difference, the volt meter on the dash is showing a between mid way to high which is pretty normal, I don't know if that's significant.

I had planned to use my car somewhere this weekend, I assume this problem means the battery isn't being charged as effectively and will eventually run out of charge all together so I shouldn't rely on it?

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Still worth measuring the voltage across the battery terminals with a proper voltmeter. Should be 13.5 - 14.5V when the engine is running. The battery will be charging if this is maintained under load - headlights, blower, HRW, etc all switched on.

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I have tested the battery and the voltage went up with main beam, CD player, blower and anything else I could find on, from 15ish to 20ish (my volt meter isn't digital).

It looks like it has leaked at some point though with a white mould-looking substance around the base, going to take it out and take a look.

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I have tested the battery and the voltage went up with main beam, CD player, blower and anything else I could find on, from 15ish to 20ish (my volt meter isn't digital).

It looks like it has leaked at some point though with a white mould-looking substance around the base, going to take it out and take a look.

There's something odd as the voltage across the battery normally drops a little as load increases. Assuming your voltmeter is working ok, I would suggest a regulator fault as the 15-20V is too high! You run the risk of damaging the battery with that sort of voltage across it.

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I have tested the battery and the voltage went up with main beam, CD player, blower and anything else I could find on, from 15ish to 20ish (my volt meter isn't digital).

It looks like it has leaked at some point though with a white mould-looking substance around the base, going to take it out and take a look.

thats not good, at no point no matter what the load should your battery be receiving 20V

sounds like the voltage regulator is dead on your alternator. being overcharged can kill a battery very quickly - possibly the reason you have white build up around the battery.

check the voltage on the back of the alternator and see what its pumping out.

as for the light, i had simillar on my 300tdi. Turned out to be the wire crimped on to the warning lamp connector on the back of the alternator had started to break away. Out of the 10 little bits of copper making up the wire, only 1 was left attached, the rest had snapped on the crimp and come away.

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I've pulled the battery out and the crusty stuff is from the battery, not good. I have done more checking, with the engine at 1500rpm and at idle, my volt meter is showing a steady 20V, no change with everything electric I can find to put on - on or off. My volt meter is older than I am, so I'm not going to trust it 100% but it shows at least the battery is not draining faster than being charged. However, while doing the tests the battery light came on as before, dimly, just after all the electrics were on. I turned off the engine and on again and it wouldn't show - what does that mean?

Here's the stupid question: which of the connections on the rear of the alternator is the D+ etc? Haynes doesn't say, as per usual.

Either way, is this going to mean a new alternator or is stripping/rebuilding the old one with a new diode pack and brushes going to solve it?

I want to get a new battery as this one is clearly damaged, but obviously I need to get the alternator sorted or it'll do the same to the new one, but I had promised to be somewhere with the vehicle this weekend. :(

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You should be able to replace just the regulator, not the whole alternator. I wouldn't drive it like that, no telling what it's going to do to the battery or what the battery is going to do when it's had enough - does it get hot for example due to being over-charged?

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An indicated 20v and build up on the battery? over-voltage no doubt. the battery is boiling and will need replacing if you've been running like this for any length of time. you may get away with just checking and topping up the battery with water.

Change the regulator/brush pack, they only cost 10 to 15 quid.

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I've replaced the regulator and topped up the battery, the voltage reading is still at 18ish for the battery, will that go down as the battery drains to a proper level or is the alternator going to maintain it at that charge? The old bushes were very worn (pictures to follow).

The battery light is still lit though, so dimly you can barely see it and it would have to be dark to notice it at all, but it is lit still. I'm stumped....

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Remember the light comes on when there is a difference of voltage either side of it. One side is the battery and the other side is the alternator, when they are different the lamp lights up. The brightness of the lamp is determined by the difference in voltages.

For example 3v in battery (nearly flat) and 13v alternator output this gives 13 - 3 = 10volts across lamp it will glow brightly.

Or maybe in your case 12v in battery and 18v alternator output this gives 18 - 12 = 6volts across lamp glow moderatly.

As your battery approaches 18volts the lamp will go dimmer until they are matched then with no potential difference it will go out.

Hope this explains it well.

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first off go and get a new meter, if its ancient it could be talking rubbish, maplin do basic ones for about a fiver.

I Mildly miffed around trying to replace diode packs etc in a Lucas A127 alternator fitted to a ford transit (very similar to the landrover one afaik), turned out after a lot of wasted time and refitting the alternator twice that the stator coil was shorted out completely, giving a nice shower of sparks when i tried to reconnect it, and i ended up having to buy another alternator.

The diode/regulator pack was £15ish, the new alternator was £50 delivered, and for the time i wasted on it it would have been more economical for me just to buy the new unit outright. Something to consider...

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The diode/regulator pack was £15ish, the new alternator was £50 delivered, and for the time i wasted on it it would have been more economical for me just to buy the new unit outright. Something to consider...

The rectifying diodes are in the alternator casing, and are much more of a faff to replace - but still do-able.

The regulator and brushes are in the pack which is mounted on the back of the unit, which is easy to change.

I agree about the multimeter, they're so cheap, everyone should have (at least) one! at last count i had four.....

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yer my repair kit had both, i had to unsolder the stator and rotor leads and resolder them onto the new diode pack.

I imagine in my case the stator coil had shorted out (probably to the alternator casing) killing the original diodes/regulator etc and therefore replacing them just took ages and wasted a lot of time.

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The problem persists despite the change of regulator, topping up the battery and cleaning all the connections on the back of the alternator. I suspect the battery is damaged so will need replacing, but I need to be sure slapping in a new battery won't just cook that one too. How do I work out which connectors are which on the back of the alternator and which ones to get a reading from using my new multimeter to see if it's over charging still? I know you have the small wire going across to a connector on the top right hand side (as you look at the back) and then a cap covering three bigger connectors at the botttom centre, I just need to know which ones will tell me what I need to know.

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