My 84 240 had the manual trans. 4-speed with an OD button for 5th. I was able to solve the same problem by just replacing the wires from the button on the shifter to the OD solenoid, They had gotten pretty bad over the years because they had been exposed to oil and the elements. first thing to do is just check the connections at the switch and OD soleniod. On my 84 sometimes the shifter ball handle would come off the shifter in my hand and would then require some careful re-assembly to get the switch re-connected and working. Hope your issue is this simple to solve. Good luck.