confusing alternator problems

Hi my disco 300tdi rev gauge stopped working at the same time the battery light flickered and was on very dim for a few minutes so I pulled over and had a look under the bonnet all seemed well but the alternator was hot and after that the battery light has not lit up since, restarted up drove home, as soon as I got home I tested the voltage across the terminals and 12.4v started up its was still 12.4v so the alternator is not charging, there is continuity between the battery and B+ the 100amp alternator fuse is in tact the battery light bulb is working yet I turn the ignition on I get no battery light and I know that if I don't get a battery light working the alternator will not charge the battery so have you got any ideas at what it can be other than the alternator itself ??

remove d+ wire from alt check it has 12v with ignition on if it has change alt

If it has lucas plug two big terminals and one small-they burn out and repair kit available.

Try fitting plug couple of times.

Small battery light wire should be 12 v ign live and w is tacho from memory.

unfortunately I don't have the lucas plug on my alternator and I don't know which wire is D+ and I cant find a wiring diagram for it on here

Two small wires are tacho and battery charge light.

Test with meter for 12volts to body earth.

The lamp should illuminate when wire earthed.

The regulator on alternator needs ignition to correctly operate.

Some produce no output and others blow alt protection diodes if no ignition feed

had a bit of a look at it and its a lucas a127 65 with a red wire disconnected and yer I think you are spot on the small brown and yellow wire produces 9.8 volts and the small white wire produces 0.3 so looks like im ordering a new alternator

CJ2a said:

had a bit of a look at it and its a lucas a127 65 with a red wire disconnected and yer I think you are spot on the small brown and yellow wire produces 9.8 volts and the small white wire produces 0.3 so looks like im ordering a new alternator

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If you earth battery light wire-does it illuminate