So first off I have read many other threads and cannot find my specific symptoms which is why I am posting this. I have a 2002 f150 super crew lariat. A while back I tried using my 4x4 and it didnt work I checked into the actuator and it worked. Checked to make sure I was getting vacuum to both selenoids and I was. I turn the truck to 4hi and the light would come on but no clicks behind dash. Then I would switch it back to 2hi no clicks and the 4x4 light remained on. Eventually after sitting a while and starting back up with it selected to 2hi the 4x4 light would be off. So I figured maybe it was the switch. I went to the junkyard and got 3 selector switches and tried that. It worked as soon as I plugged in the selector switch everything engaged I could hear a click then a clunk of the actuator engaging. And the front wheels had power. Went back and forth a few times from 2hi to 4hi and it engaged and disengaged corecttly and the lights on dash worded correctly. I drove it about 30 minutes came to a stop and tried it again. i switched it to 4hi heard a click but no clunk from the actuator and after trying to switch it back to 2hi no clicks and the 4x4 light remains on. at this point I am convinced it is something in between the switch and the vacuum sulenoids electronically but not sure. Any help would be greatly appreciated and thanks in advance and this is electronic shift not manual

 

Very likely the fire wall solenoid is sticking.
You need to put it in 4h and test for vacuum to the front actuator, when it fails.
Good luck.