The side that is not working correctly has a bad ground wire and is most likely at one of the sockets. You have to check to make sure all these wires, especially the ground wires are connected tightly and are clean. The current is finding another path to ground and is why you have this erratic light behavior.

Try grounding the socket with a jumper wire or something and see if that works. All of the light wiring runs thru 2 connectors which are located on the turn signal arm. You must remove the covers upper and lower from the steering column. This is not hard but be careful not to cut the hair security wire on the lower half. If you do the truck will not start and you will have to tow it to the dealer ( found that out the hard way). most probably you the plastic tabs inside the wire connectors on the turnsignal module broke. This is from using the tilt steering. You can just buy the connector itself from ford and redo all the connections. Just take your time there are a lot of wires in there but this is not a hard fix but yes its very much time consuming. This will help. Thanks please keep updated.please do rate the solution positively .thank you for using fixya.