You might check with the IPD web site. They have a subsection within the Volvo 200 series that deals with transmissions, and they have at least one item there that deals specifically with the automatic tranny overdrive. It says:
"Automatic Over-Drive Solenoid Bypass Kit
If the overdrive has stopped functioning in your 1983-1995 240, 740 or 760 with automatic transmission we now have an economical fix for the most common failures. The most common failures are the relay ($48), the solenoid ($144) and wiring which can run well over a hundred dollars to trouble shoot and repair. Our new Solenoid block off kit, bypasses the entire system and allows the trans to shift in and out of overdrive automatically. How many times have you used the OD button on the shift lever to shift down for hills or while towing? It’s really not necessary for most drivers."
I hope that helps