No ignition / battery light

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Defender110
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No ignition / battery light

Post by Defender110 »

The wife rang up earlier stranded with a flat battery, In ran out with a replacement to get her going but noted there was no ignition / battery light iluminating. I put a meter across the battery and it is not charging. I seam to recall that if the ignition/battery bulb is blown this will break the charging circuit, Is my memory correct or should I be looking elsewhere? I need to try and fix this tonight so any quick replies would be very much appreciated.
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mat_fenwick
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Re: No ignition / battery light

Post by mat_fenwick »

You're correct, chances are if you replace this bulb then it will charge again.
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Defender110
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Re: No ignition / battery light

Post by Defender110 »

Thanks Mat, I'm on with it.
Kevan
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citsncycles
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Re: No ignition / battery light

Post by citsncycles »

That's today's something new learned - I thought it was only old British stuff which worked that way.
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Re: No ignition / battery light

Post by Defender110 »

Just swapped bulbs with the water level lamp that was working and no joy, still no battery light :-(
Kevan
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mat_fenwick
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Re: No ignition / battery light

Post by mat_fenwick »

citsncycles wrote:I thought it was only old British stuff which worked that way.
:oops: I don't know for certain the BX does work in this way, but assumed all cars did...

I'd check the small wire is still attached to the back of the alternator then - they can sometimes get brittle with heat/age and break off.
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Re: No ignition / battery light

Post by Defender110 »

Yes small wire still attached, i've checked the alternator output with the engine running and the main wire is showing current battery voltage of 12.2v and the little wire is showing 11.35v?


EDIT; left it charging overnight so she will have a charged battery for tomorrow then i'll have another look over the weekend.
Last edited by Defender110 on Thu Oct 11, 2012 8:17 pm, edited 1 time in total.
Kevan
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2003 Land Rover Discovery Series 2 Facelift TD5 - Daily driver / hobby days and camping.
1993 Land Rover Discovery 200tdi Series 1 3 door - in need of TLC
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JayW
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Re: No ignition / battery light

Post by JayW »

Try the single wire on the back of the alternator (usually green), it tends to crap up or fall off.

Your other main possibility is the regulator or diode as any other non-charge fault would light the lamp.
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JayW
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Re: No ignition / battery light

Post by JayW »

Damn my procrastination! Men can multi-task, honestly!
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Re: No ignition / battery light

Post by Defender110 »

Thanks Jay, I take it the reg is built into the Back of the alternator on a BX? I'll whip the alternator off on Saturday morning, how do I test the regulator & diode?
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JayW
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Re: No ignition / battery light

Post by JayW »

Yes, the regulator is the black plastic "box" on the back.

Simple diode testing is with a a multimeter. Resistive testing at approx 2k OHM should give reading one way but not the other. Resistance both ways indicates a short & none both ways indicates open.

If any of the windings are shot or the brushes are gone the lamp *should* be lit.
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JayW
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Re: No ignition / battery light

Post by JayW »

Forgot to add, didoes need to be out of circuit (disconnected) to test.

Also, have you checked the voltage of the exciter wire without the engine running but ignition on?
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electrokid
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Re: No ignition / battery light

Post by electrokid »

i've checked the alternator output with the engine running and the main wire is showing current battery voltage of 12.2v and the little wire is showing 11.35v?
Yes alternator is shot in some way - when charging the battery volts will be in the region of 14v. The 'ign' bulb is driven directly by the little wire connection - AFAIK its operation - or non operation doesn't affect the working of the alternator- it's an output from the alternator only.

If Jay's checks don't prove fruitful then I suggest an eBay search for a replacement.
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JayW
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Re: No ignition / battery light

Post by JayW »

electrokid wrote:[it's an output from the alternator only.
It's always been my understanding that this wire feeds 12v to the field coils (through the idiot lamp) to excite the coils and create the electromagnetic field required to produce power. If this wire is not supplying 12v then the alternator won't charge. Many alternators will self-excite once the revs get high enough (2k-3k).

As the bulb has been substituted for a known god this is unlikely to be the fault (unless there is a wiring issue). Most internal alternator faults which stop the production of power return this wire to ground and light the idiot lamp, hence my only suggestion of the diodes.

An alternative to test the wiring to the idiot lamp is to connect a spare dash bulb between this output terminal on the alternator and battery positive which should act exactly as the dash light should. If it does this indicates a wiring fault between the alternator exciter wire and the dash bulb circuit.
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electrokid
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Re: No ignition / battery light

Post by electrokid »

It's always been my understanding that this wire feeds 12v to the field coils (through the idiot lamp) to excite the coils and create the electromagnetic field required to produce power.
That used to be one arrangement but not these days AFAIK the lamp connection is just that - an output from the alternator to drive a lamp when there's no alternator output - everything these days is self exciting. (Unless you've got a Granada with a nasty Pierburg electric choke in which case the little wire on the alternator is a 6 volt output to the choke system :shock: )

Anyway back to solutions to the problem - this eBay item ends tomorrow about midday but it'll probably roll over - very reasonable price.

http://www.ebay.co.uk/itm/190667118300? ... 1438.l2649
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