2001 Ford ranger will not go in 4L

I have a 2001 Ford Ranger 4x4, when I put it in 4H it goes in. When I switch over to 4L it does nothing. I put a new selector switch in it and it still does the same thing. At one time it would go in both 4H and 4L, then i had to click it in 4L a few times before it would go in. Now it won't go in 4L, is this a relay problem or something else??