I agree with Bob - check out the contacts etc. at the non-working bulb(s).
Did you already test the bulb itself or try replacing it? (notes below on getting at the center high bulb)

And do you get the bulb-out indicator when you step on the brake?
Does the bulb-out indicator come on just before starting the car - in other words, is the indicator bulb alive??

Our '90 sedan has dual rear "fog" lights. If I recall they are in the upper center positions. Dead fog light bulb does not "trip" the bulb failure warning system.

I'm guessing your car is a sedan - they seem to have more trouble in the rear lights than the wagons. Yours is a sedan??

Sedan center high bulb - I had trouble getting at mine. See the owner's manual. If your manual is missing, visit http://www.volvocars.us/ or
www.volvousa.com
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Sven: '89 245, IPD sways, electric rad. fan conversion, e-codes, 28+ mpg - auto tranny. 850 mi/week commute. '89 245 #2 (wifemobile). '90 244 (spare, runs).