Volvo Repair: 93 940 overdrive problems, fuse panel, relay switch

Question
my '93 940 Sedan won't shift, gets stuck & won't let the overdrive kick in.  running the engine @ a high rpm, while going going down the highway..kicks in & out at will...is there a sensor or relay switch that needs to be replaced, if so where and how.  can i do this or does a mechanic have to do it.
Thx for the reply...

Answer
if the light goes on and off when this happens then it is an elecrtical problem is is most likely the relay if the light stays off when this happens it may be a bad solenoid or problem in the transmissionbelow is how to change the relay.


e overdrive  pump relay is located on the fuse panel behind the ashtray.remove the ashtray and then remove trim around lighter socket then you will see 2 screws remove the screws and the storage area will come out the relay is white and about 1x1x3  inch.it will be towards the passengers side of the panel.