Jeep Grand Cherokee Transfer Case Disengage

Light Indictor Says It's Out Of P/t 4wd, But Still In. Unless I Drive In Reverse For A Bit, Then It's Out - Why? And What Can I Do?

I Think The Problem Is On Going, I Bought This Jeep With A Front Diff. Pinion Bearing Out, I Replaced It With A Low Mile 3.55 Ratio Out Of A...