Alternator lazy?

Hi folks. The first job I need to do I think is replace the alternator on my legnum.

The battery discharges and goes dead while the engine is running.
Putting a multimeter to the battery shows only 12v or just over but the battery light doesn't come on on the dash.

Would I be right in thinking the alternator is putting out just enough current to satisfy the warning light and not much else (lazy), or is there another issue that I might be overlooking?

Also, I've got a 100amp fitted presently and considering upgrading to a 120amp version sourced from viamoto.

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Does the battery light come on with the key before starting engine?
if not, try replacing the bulb. this might fix everything.

^What he said, if the bulb is OK look at the main wire from the alt to the battery and the big fuse for corrosion / breakage / damage. Voltage should be about 14.4 volts with the engine running and no excessive loads like lights draining from the system. If all is Ok in the wiring / fuse the brushes in the alt are most likely worn right down and need replacing, this could cause the battery light to not come on too since the bulb provides the start-up current for the field via the brushes.

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Originally Posted by Amonlym

Does the battery light come on with the key before starting engine?
if not, try replacing the bulb. this might fix everything.

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I recall the bulb light coming on in the past, but I had to move the car a day or two ago and I cycled the ignition 3 or 4 times and I couldn't see a battery light at all anywhere.

I assume there's a guide as to how to safely remove the clocks to check? Or is it pretty darn obvious?
I didn't really look as I had an excitable American bull dog thinking she was going for a car ride! Ha ha

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Originally Posted by Tony_T

^What he said, if the bulb is OK look at the main wire from the alt to the battery and the big fuse for corrosion / breakage / damage.

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Hi Tony - just a quick question on this as I have a similar problem with the alternator not working - is the big fuse the yellow or the blue one in the engine fuse box?

Many thanks

@russhowe I don't have a wiring diagram but before you go pulling the instrument cluster look for any other fuse which may feed that lamp. If you do want to pull the cluster just take out the two screws that hold the trim above the cluster and remove that, then you'll see how the cluster is held in (it's years since I had to pull one of mine) but at least there is no fighting with a speedo cable to detach it like in some cars. I recall it is easy.
@Judder I can't help on that, my response above was based on general principles of alternator operation not of specific locations for our cars. I had a quick look at my remaining Leggie but it is very hard to see anything without pulling other bits off which I won't tempt fate by doing! I suspect if the fuse is actually blown you'd see that but corroded wiring could be very hard to spot. If you can get to the battery terminal on the alternator without pulling half the car apart or doing yourself a spine injury, measure the voltage on that terminal (with respect to the vehicle body) with a meter or even a test light with the engine NOT running, if the fuse and wiring are OK the reading there will be exactly the same as if you measure direct across the battery. As another thought, check the main earth wires from the engine block to the body and from the battery to the body for any looseness or corrosion. The most likely thing though is always the brushes as they are subject to constant mechanical wear. These should be easily checked and replaced if necessary but you will need the alternator out of the car to do it and that's the bit that won't be easy.

I pulled the cluster and swapped the oil pressure light bulb and battery light bulb around, as I knew the oil pressure light was working fine.

Flicked the ignition light on and still no battery light.

Checked the fuse box under the bonnet behind the battery and all the fuses visually look ok.

I metered the two fuses on the far left of the fuse box and got continuity but no voltage.

Anything look out of place to more experienced eyes?

I'm a cats whisker away from buying a new alternator and replacing the battery lines all the way up along with any earths along the way.

Edit: realised I went on to talk utter nonsense regarding a relay, pointless paragraph removed.

What do you all reckon?

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Something isn't right. You should have a battery light with the engine not running. I can't understand why a dodgy alternator would stop the battery light coming on.

Can you check the main cables where they come into the fusebox? The bolts on the fuses on an angle, bottom left on your photo.

The one at the bottom right has a battery symbol as well. I don’t know what it’s for but from watching the picture of the cover there is a battery symbol for that fuse/relay as well.

https://www.clubvr4.com/forum/showth...907#post825907

Check that thread for additional ideas. we went into some detail on the overall charge circuit

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Originally Posted by Nick Mann

Something isn't right. You should have a battery light with the engine not running. I can't understand why a dodgy alternator would stop the battery light coming on.

Can you check the main cables where they come into the fusebox? The bolts on the fuses on an angle, bottom left on your photo.

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The bolts under the blue and yellow fuses? 60A and 100A. They look pretty clean, *very* minor corrosion where the cable is held by the crimp terminal.
Couldn't remove the fuse easily so I gave up in fear of breaking something.
As I said earlier I got continuity through the fuses so the fuses themselves are (I think) ok

Surely if the power cables to the fuse box were at fault I'd have all sorts of other issues? All my working warning lights go off as they should (ABS/TCL/AYC etc)

I'll certainly have a look though next chance I get

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Quote:

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Originally Posted by Bobby~d

The one at the bottom right has a battery symbol as well. I don’t know what it’s for but from watching the picture of the cover there is a battery symbol for that fuse/relay as well.

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Yeah I wasnt sure on that one either.

Once I get the car to my home address then it'll be easier to fiddle around with things and diagnose what's what.

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Also while I think of it, before the car came off the road the battery light was showing intermittently. So something somewhere was either slowly failing or a connection only making partial contact.

But I agree it's strange to not have a battery light at all!!
Unless the cluster is faulty perhaps? The bulbs a certainly working fine

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Quote:

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Originally Posted by Amonlym

https://www.clubvr4.com/forum/showth...907#post825907

Check that thread for additional ideas. we went into some detail on the overall charge circuit

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Thanks very much! Some good stuff there and gives me something to work from. Much appreciated [emoji846]

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Quote:

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Originally Posted by russhowe

The bolts under the blue and yellow fuses? 60A and 100A. They look pretty clean, *very* minor corrosion where the cable is held by the crimp terminal.
Couldn't remove the fuse easily so I gave up in fear of breaking something.
As I said earlier I got continuity through the fuses so the fuses themselves are (I think) ok

Surely if the power cables to the fuse box were at fault I'd have all sorts of other issues? All my working warning lights go off as they should (ABS/TCL/AYC etc)

I'll certainly have a look though next chance I get

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The bolts hold the fuses in. I've had an issue in the past with an intermittently illuminating battery light and it was a loose connection on one of the cables that bolt in there.

things in circuit for battery indicator:
battery +, fuse, ignition switch, indicator lamp, a diode, pin L on alternator, alternator voltage regulator, ground.

Other things on the connector plug:
Pin S - direct B+ feed,
FR and G go to the ECU.

The bottom right battery symbol should be the alternator relay.

simple multimeter tests with key on engine off:
you should have 12V to ground on S, but significantly below 12V on L
you should have 0v between the alternator output stud and B+

Quote:

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Originally Posted by Tony_T

As another thought, check the main earth wires from the engine block to the body and from the battery to the body for any looseness or corrosion. The most likely thing though is always the brushes as they are subject to constant mechanical wear. These should be easily checked and replaced if necessary but you will need the alternator out of the car to do it and that's the bit that won't be easy.

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Thanks Tony - advice much appreciated and I'll carry out some of the tests as you say when I'm back with the car :thumbsup: