Volvo Repair: Overdrive relay switch, 1991 240DL Wagon, center vent, relay switch

Question
The overdrive light (which looks like an arrow) won't go off on the dashboard, and the car will not shift into 4th gear as a result.  The solenoid and button were changed but to no avail.  Someone suggested that it may be the relay switch.  If so, where is it located, as I cannot seem to identify it in my Chilton's repair manual.  Thanks.  

Answer
First thing is check all fuses, if they are good, remove the glove box and look for relay sitting behind the center vent. Sometimes the clip securing it causes the contacts not to operate. Remove relay from clip and check to see if it clicks when the button is pushed. Either repair relay or replace, I usually just replace it, about fifty bucks.