Volvo Repair: 1989 240 dl sporadic overdrive, vent area, center vent

Question
Hey,
I bought a 240dl. I have a orange/yellow arrow light on the gauge panel somtimes it goes off and kick's into overdrive, for the most part it stays on and, no overdrive. Can you help?
Thanks

Answer
most common would be a bad overdrive relay below is how to replace it.

remove the screws holding the glovebox in then remove the box and look towards the center vent area in the opening where the box was and you will see a white relay.lift up on the relay to unclip it from the dashboard.new relay about 55 dollars.