I searched the site, but could not come up with an answer, so here goes.

All three brake lights have gone out on the wife's 1997 850 sedan. Since the transmission will switch out of park with the brake pedal depressed, I am guessing that the brake pedal switch is OK. Elsewhere I have read that there is a bulb relay located near the driver-side rear light cluster. I believe I have found the blue box in which it is located, but can't quite figure out how to open the box without breaking it. Any suggestions?

Thanks.

 

Any luck in your problem? I have the same problem with a 97 850 wagon.

 

I found the blue box. It is the stop light relay switch as indicated on the box itself. You can open it by prying off the back cover with a flathead screwdriver. But, you don't need to open it up to test for continuity. With the blue box unplugged, use your multimeter on 54 and 54R first and then 54 and 54L next to test for continuity. You can also test make sure you are getting 10 to 12 volts by using your multimeter on the wires that are going to these three prongs. Mine tested fine.

See my thread in case yours is fine as well.

https://volvoforums.com/forum/volvo-850-16/no-brake-lights-97-850-wagon-49918/