having trouble getting trans to shift to overdrive

have you tried pushing the button on the end of the shifter,on,off,on,off? is the OD light on? if you have tried that and it makes no difference,then it could be a bad OD switch,end of shifter or>>>If it has tilt steering there is maybe a wire chafed in the steering column. Take the covers off and follow the wires where they come out of the shift lever.