Greetings, I have a 2000 S80 with some lighting problems that are driving me nuts.
ALL of the rear bulbs burned out, I assume, at once. Replaced all bulbs, but nothing. Checked the usual suspects (relay, fuses, etc) to no avail . All the sockets look pristine , no corrosion, no burns.
Not sure if related or separate, but when running, the headlights flicker, for lack of a better word and an audible click can be heard. Any help would be appreciated. Starting to think I should have stayed with my Dodges lol.

 

clicks sound like a relay issue but could also be the ignition switch acting up. Check out volvowiringdiagrams.com to have a look at the connection paths and what's in play. Note some of the relays are internal to the CEM which may be the culprit, but you'd need to check voltage at the pins to diagnose.

 

Did you actually test the bulbs to determine that they were all burned out versus no power going to the bulbs?

The only way that I can see that all of them were burned out was that they were never changed.