I have a 97 F150 Centurion Edition when I got the truck the 4x4 shifter would be in 2h well the 4x4 would kick in on its own and it would make this grinding noise I unhooked the vacuum solenoids to keep it in 2h well sometimes when I drive you hear a clicking noise right in the middle of the dash right behind the radio and the 4x4 light will flash on and off from what i've read people say it's the gem module is there something behind the radio that controls the 4x4

 

Bud, you've got to get a Chilton or Haynes book...

It will help you much more than you think.

 

above glove box is auxiliary relay box #3
It contains parking lamps relay, headlight relay, and .......transfer case relay

By disconnecting the vacuum, all you did was keep the front axle from engaging.
The transfer case is still shifting into 4x4

pull the fuse to keep this from happening.

after that, troubleshooting the system isnt easy due to the GEM module and speed and transmission inputs . It could be a bad switch, or a broken wire that is grounding out and causing the relay to trip, but it wont be simple to figure out. Its really best to pay the dealer to pull the codes IMO.

assuming its shift on the fly.

 

I believe you may have better luck in the pre-1997 or on a bronco forum. I believe all centurions were converted broncos turned 4 door and labeled with the f-150 badge(although the broncos ended production on 96 so idk..) Either way, it's the older body style and the members there can help better.

Also, those are badass vehicles. Here's a pic for those who don't know what centurions are.