The Patrol transfer case, as many others with 2 levers for low/high and 4WD, have an interlock mechanism that prevents shifting into low gear without first engaging the 4WD.
Years ago I decided with my brother, to get rid of this mechanism, and allow low gearing in dry surface conditions. After reading the posting about the PeerlessPatrol- FourWheeler Magazine Dec 1992 where the owner removed the interlocking mechanism, I thought that I had posted before. It was probably at the other forum, since the pictures are still in the Photobucket hosting site.
Please refer to the following picture from the parts manual, at the front of the transfer case, showing the levers among other things. There are four steel balls that act as detents for the levers' position. Also refer to the cross section that follows. Under plug marked with #78, there is a spring and a ball #73 (in red) There are two plugs #78, one for L/H and the other for the 4WD. They are the same red balls in the cross section below. Also present are two additional balls #73 that are located in a horizontal hole with the plug #74 in the parts diagram. These are the green balls in the cross section. The blue circles correspond to the rods that move the forks of L/H or 2WD/4WD.
Unless the 2WD/4WD lever is engaged into the 4WD position, the green balls will prevent moving the lever for L/H. The simple process of removing the interlock mechanism is to dismantle the front of the transfer case and get rid of the green balls. Like you forget to put them back
The rod for the 2WD/4WD will have to come out at least, to allow removing of the green balls.