Volvo Repair: 91 740 rear brake lights, light sockets, spring base

Question
Just recently on my '91 740 sedan non turbo,only the upper window brake light is functioning. There is no warning light on my dash indicating a problem however both rear tail lights are not working,all other lights work in the rear light housings .I have changed the brake fuse and all bulbs and checked for power in the brake light sockets and all seems to be fine.I cleaned out bulb sockets and pulled up spring base slightly thinking there was a connection problem but no corrosion was found.No work has been done on my car other than a recent oil change.I am using the krypton gas nickel plated bulbs rather than the brass based ones.Since the  upper brake light is working i didn't think it could be a relay problem ? any adivice or help is most appreciated
thank you  

Answer
Calvin, on the 90-91 740's the black circuit board is a little tricky.  With a pry bar or something holding the brake pedal down, remove the black assembly from the tail light assembly.  With a small screwdriver, press down on the silver material where the brake bulb is and see if it lights up.  The contacts pull up from those.    Common problem on these.  They are reasonable.  I would order new ones from the dealer.