1996 t100 3.4 auto 4x4. When I first start the truck the light is not on if I take it out of park and put it back in park the light comes on. The truck drives forward but it won’t really go anywhere in reverse.

if I put it in 4hi the light goes out in park but I still don’t move anywhere in reverse.

what would make this light come on when my transfer case is in 2hi and not neutral?