If it worked before you stored it, do as john indicates in his test.

Then if the solenoid on the OD does not click, pull the shift lever further to the right and rear. This may be enough to get the 4th gear switch to make contact.

Your power route is fuse, relay controled by stalk switch, from relay it splits, one wire to indicator light, one wire to switch on trans then to OD solenoid, then to ground.

If you can get juice to the solenoid and it clicks, then the problem is dry hard actuating piston seals from not being used for a few years. To replace them the OD has to come off the tranny.

Duane