Alternators, Exciters & Warning Lights

[nsblue]

Hi, I'm looking for some insight into the following:
2001 Volkswagen Lupo, SDI. Bosch alternator.
Battery light came on whilst driving. Measured 12.8 or so at battery terminals whilst running so not charging.
Ordered replacement alternator to fit and in meantime charged battery before unavoidable journeys to work and back.
Battery light now does not come on with ignition key, whilst engine runs, or after engine stop.
My understanding is that (in general) the battery light on dash is in circuit with the exciter component of an alternator.
My question is can an alternator (in general) fail in such a way that the light will not illuminate at all?
I suspect (hope?) that the replacement alternator and a clean up of some visibly corroded connectors to the posts will solve the problem but I would appreciate some general insight and advice into what's going on for future reference.
TIA.

[Rich]

The light in a 2001 Lupo will be an LED driven by a controller in the dash so not a part of the circuit like it used to be. Sounds like a faulty alternator to me. All you can do it check a wiring diagram for the car really just to be sure.

[nsblue]

Thanks for the reply Rich.
Yes, I'm expecting to fix the battery light issue with the replacement alternator.
I understand that the light is an led in the cluster and I'm assuming it's not coming on at all due to broken circuit somewhere, perhaps in the regulator end of the alternator. If replacing the alternator doesn't sort it I'll start deciphering the wiring diagram.
I suppose I'm asking for insight as to whether or not this is a typical symptom of a duff alternator or bad wiring or a bit of both.

[Rich]

Mar 20, 2022 19:18:06 GMT nsblue said:

I suppose I'm asking for insight as to whether or not this is a typical symptom of a duff alternator or bad wiring or a bit of both.

A little from column A, a little from B but I suspect that it's more likely a failed alternator in this case, they can cause failure to light the GEN warning on total regulator failure, if the reg is 'saying' the battery voltage is less than the GEN output then the light won't come on. Even if that isn't true.

[nsblue]

Mar 20, 2022 19:30:45 GMT Rich said:

Mar 20, 2022 19:18:06 GMT nsblue said:

I suppose I'm asking for insight as to whether or not this is a typical symptom of a duff alternator or bad wiring or a bit of both.

A little from column A, a little from B but I suspect that it's more likely a failed alternator in this case, they can cause failure to light the GEN warning on total regulator failure, if the reg is 'saying' the battery voltage is less than the GEN output then the light won't come on. Even if that isn't true.

Thanks Again.
This is just the sort of insight I'm after: That alternator failure can cause the GEN warning to fail to light rather than it being more likely to be a separate but coincident fault.

[silver63]

Might be worth checking if it is a fuse as a lot of vw from that era have a fuse box bolted too the positive battery terminal with abs,alternator and internal fuse boxes fed from .

[nsblue]

Mar 20, 2022 20:20:23 GMT silver63 said:

Might be worth checking if it is a fuse...

Thanks silver63 rich

New alternator solved the problem.