it is stuck in 4h on 1991 Mazda B2600

I have a 1991 madza 2600 i thats stuck into 4 high and will not go into 4th gear

Asked by for the 1991 Mazda B2600
Manual transmission will not shift into 4th?

Is this a push button 4x4 system - electronic? Or a manual lever pull? If it is the push button, the motor that switches the transfer case position could be failed.