The fact you have a grinding noise when placing in park tells you the output shaft is turning. I would have to say either the transfer case if bad or the collar where the shaft goes in is stripped the only other possibility I can think of is the rear planet splines are stripped out. Its not an electrical issue

 

Something in the t case broke. Output shaft spins freely no matter what gear the trans or t case is in. And it was full of fluid. I filled it when I installed it. Just drained it but saw no metal. Maybe a snap ring or fork in the t case broke? Hoping I have parts from my old one to make one of them work..