Battery light staying on

Just got a 1991 range rover classic with a 3.9 v8. At the weekend the battery came on and stayed on after start up. Rev of the engine didn't clear the light. Checked the alternator was running and it was. It was also kicking out 13.9v. Measured at the battery.
The light is on dull, foot on brake and it will sometimes come bright. Sometimes won't. Put all lights on and it will go brighter.
Anyone any ideas? As far as I can tell the alternator and battery is fine and the battery is charging.
Not long had the car so any advice would be great.
Cheers all

Generally speaking, that would indicate a duff alternator regulator/diode pack, on a P38 it could also be a bad connection from the alternator to the BECM, don't know if the Classic has such complications.

I've had this before - your alternator needs some TLC. I assume being a '91 you'll have a Lucas A133/80. A replacement alternator will be expensive if you can find one.

Find a local auto electrician and ask them to give it a rebuild unless of course you are happy to do it yourself, it isn't that hard.

It isn't that expensive and I would strongly suggest you go for new regulator, brushes and slip rings. Worst case will be you need a new armature; had to do that on one of my alternators a couple of years ago but it was cheaper than a new alternator and made it "good as new".

Trust me on this, don't leave it - get it sorted ASAP or you will have problems that you don't want or need in winter.

Oh and Datatek, no BECM on a classic so no issue in there but like most things Range Rover an iffy alternator or battery can cause all manner of headaches that are not immediately obvious as being a battery/alternator type issue (been there!).

A kit like this will do the job.

ALTERNATOR REPAIR KIT FOR LUCAS A133 UNITS 3 SPADE PLUG TYPE RECTIFIER TYPE | eBay (no affiliation and not used this seller). Just make sure you get the kit with the right connections for your alternator.

I refurbed the alternator on my 1988 Classic using a kit containing similar parts - a straightforward job, I just need to buy a heftier soldering iron.

Pete

if the alternator is kicking out 13.9 v then it may be ok, it could be a short on the battery light wire, disconnect it from the alternator (generally the single small wire) put a test light on the + side of the battery and put it on the alternator where the wire plugged on, with the engine off it should light up, with the engine running it should go out. If it is dim or doesn't go out then its deffo an alternator fault, if it goes out its a short on the light wiring.

kev1nlm said:

if the alternator is kicking out 13.9 v then it may be ok, it could be a short on the battery light wire, disconnect it from the alternator (generally the single small wire) put a test light on the + side of the battery and put it on the alternator where the wire plugged on, with the engine off it should light up, with the engine running it should go out. If it is dim or doesn't go out then its deffo an alternator fault, if it goes out its a short on the light wiring.

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if it wasn't the alt, but a short on the battery light wire, then unplugging it from the alt would mean it would still be on and thus proving your theory. no?

trax said:

if it wasn't the alt, but a short on the battery light wire, then unplugging it from the alt would mean it would still be on and thus proving your theory. no?

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Yes.

yes that's true but only if there was a short from the light to the alternator, it wouldn't rule out a possible PCB fault within the dash that may cause the fault on the light. I just like to be thorough

No harm in re-furbing your Alt as the cold heads our way. Another worth checking is your connections from starter motor to solenoid. Make sure they are clean and secure, the hefty brown wire from the Alt needs a good connection so get under and get it done. A small coating of petroleum jelly wouldn't go a miss either (Vaseline)

I would also fully charge your battery with a charger to give it a health boost. As said, RRC's don't work well on a poor battery or Alt.

Good luck

DC_ said:

As said, RRC's don't work well on a poor battery or Alt.

Good luck

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You been there too then