Volvo Repair: 1992 Volvo 940 Turbo, solonoid, 1992 volvo 940

Question
The auto tranny shift has a button on the side that shifts the trans. into overdrive. When it is locked out in 3rd gear, an arrow lights up on the dash. The car is locked in 3rd, and pushing the button will not allow it to go into overdrive. Can you tell me if there is a switch replacement repair, is it the solonoid? or something else more expensive? The speedometer is also working erratically, and when the solonoid on the tranny is wiggled, the speedo will jump to 40 mph standing still.
Any help you can give will be appreciated.  

Answer
Don, remove the ashtray assembly and remove cover for cig lighter. Remove 2 screws and remove that panel.  Replace the white relay to the right.  Its the O/D relay.  Start with that first and also check fuse.  The speedo issue is coincidental.  You probably will need a new speedo head.  Common problem on the 940's.  Roger