Volvo Repair: 4th gear disengaged, light flickers, fuse panel

Question
I started my 1991 Volvo 240 sedan yesterday and the "4th gear disengage" arrow indicator was on and won't go off. The car is running as a 3-speed and won't upshift into the 4th gear. The car is has fairly low milage for a Volvo (120,000) and I hadn't noticed any other problems with the transmission. The rear window defogger stopped working the same day.  

Answer
Hi Lisa,
      Check out your fuse panel to see if any are burnt out...be sure all fuses are very clean at  the ends..
      Your tailgate defroster may have a broken wire...located in tailgate upper hinges...they often fail at this area...it is a job that can be done if you can solder wiring....after carefully removing the hinge..
       The transmission problem is probably  related to a overdrive relay....easily replaced...it sits behind dash board next to  glove box toward  center...take out 6 screws holding  glovebox...feeel behind dash for square relay...sometimes its stuck there and you  may have to yank a little to be able to see how to unplug it...I think its white...maybe orange?
          With you driving car...over 45mph...have a friend tap on relay with a med sized screwdriver...if light flickers or goes out...you need a overdrive relay..if it stays on you may have broken wiring at gearshift...unlikely...the od relay is the problem...unless you burnt out a fuse.
          If you need a relay...buy it on net...save lots..
                 Good luck,
                   Bilbo