4x4 jumps out of high

[Feddersen]

My 2003 Sport Trak doesn't engage in 4x4 high correctly. It will shift to high but seconds later will snap and go back to 2 wheel. It will snap back and forth every 15 seconds or so. Any suggestions greatly appreciated.

 

[oklagp1200r]

My 2003 Sport Trak doesn't engage in 4x4 high correctly. It will shift to high but seconds later will snap and go back to 2 wheel. It will snap back and forth every 15 seconds or so. Any suggestions greatly appreciated.

Could be the relay or the transfer case motor (the switch motor on the transfer case). Do you physically here the motor on the case engaging when the dash switch is placed in 4x4 high?
What about low does that work or act differently?