It seems that the Volvo engineers were at fault here. The dimmer switch for the instrument cluster includes all of the dash lights as well as the center console. The problem there is that the rheostat will allow 14V+ (alternator output) when on the maximum setting and the bulbs will burn out at about 5,000 hours or less.

The shifter bulb, ashtray, lighter, are at 14V as they do not go through the rheostat and are subjected to the alternator output. These bulbs are always on when the headlight switch is turned on (DRL exempted). Because the ignition switch turns off the headlights when the engine is turned off, many owners leave the headlight switch on permanently, decreasing the life of the 14V bulbs.

It's too bad that LEDs cannot be used instead. It is difficult to find LEDs that are small enough to fit in the tight spaces. Perhaps "B.B." can find a solution, as he is well into replacing all of the other lights in his 850 with LEDs.

Reminds me of the 240 problem, the tiny bulbs in the rocker switches creating so much heat that the switches melt or deform. Someone solved that problem with LEDs.
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My back feels better when I sit in a Volvo seat