Well I just put the 850 on the road after 13 months (i drove other cars, and was doing 850 maintenance repairs). So I can't say for sure WHEN this started. Then it took me a month to drive it at night for the first time. The dash lights went off after ONE second after startup and turn-on. I played with the switch and the dimmer. It seems that if I play with the rotary light switch, maybe shut the car off the dash light give some momentary light upon restart - but just once. They're not coming back on after more playing with the controls. Some web searches point to the light switch or dimmer - but I don't think this momentary working points to that direction. Maybe one of those mysterious electrical components like a 'capacitor' is kaputt. This is something I'll have to fix over the next 5 years, no rush. Any ideas?

+2 on the dimmer switch. Don't try to pull it out from the front, you will damage the vinyl. Pry up the speaker cover. the rear of the dimmer switch will be uncovered. Using a finger, push the dimmer switch forward to remove it.

I don't know if I have a spare or not.
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Keeping it running is better than buying new

Looking good based on me just turning on parking lights for 2 minutes. The speaker tip was good, a fellow like me needs all the help i can get. It even looked like the speaker wires were disconnected so maybe I'll have better sound.

On my 1998, the magnet on the bottom of that speaker fell off! It took a good while to find it. And industrial strength glue, which is still working today.
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Keeping it running is better than buying new

My guess would be the dimmer switch.
Why does a simple rheostat have to be so complicated...

Tried attaching the photo in the previous post

I was going to do some test from the web on bypassing the dimmer, but it was cheap enough to get a used one. My son the electrical engineer is home for a few days, I'm hoping he might be able to tell me which little gizmo on the board went bad.

+1
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Will I buy another Volvo??? We'll see....