Volvo Repair: 1990 volvo overdrive, volvo 740gle, red arrow

Question
I have a 1990 Volvo 740GLE with automatic transmission. It will no longer shift into overdrive. The red arrow is on the dashboard and you can mash the button on gearshift all you want and it won't go off. I have change the button in the gearshift thinking this might help, but no. Just once in awhile it might work but light never goes out. Any help would be greatly appreciated.

Answer
Steve, I would start with the relay but since the arrow is going on and off  that means the relay is working.  Most likely its the Solonoid on the trans.  If you replace that and it still doesnt work then its an internal fault in the transmission.  Roger