Posting in this forum as it's a 2001 (Y) S80 D5 although this could be something on any car...

The background is that, a few months ago the alternator failed and has been replaced with a new Lucas unit. It has been checked on a voltmeter and also on VIDA and the output is 14 volts. Anyway, since the alt fail and subsequent replacement, whenever I brake I get the "Check brake lights" warning message which goes off when I'm not on the brake. Also, if I switch the headlights on I get the Position light warning (I can't recall the actual wording but it's the one that means one of the lights is out). Again, when I switch the lights off the message goes off ... just as well because that is now an automatic MOT fail.

Anway, I have checked and replaced all bulbs and cleaned the contacts. I have had VIDA plugged in an no messages/codes are showing that can be cleared and reset. I have checked the relays, disconnected the battery and still the messages appear.

Has anyone ever encountered this and, if yes, what is the solution?

Thanks for reading and for any proven solutions.