I just bought a used Ford 500 AWD. What kind of fluild goes into the rear end?

I don't know but I bought a 2006 used and someone had put red transmission fluid in the tranny and thats a BIG no no. It was a 600 dollar job to change it to Blue fluid (the correct one) and not a minute too early. Dealer and my mechanic said I averted disaster by catching this early. Sorry I can't help with your real question but it is a good one and I wouldn't let it alone.