I had the pleasure of fighting with the secondary latch today when trying to change a flat tire!!!  Sooner or later you too will have to deal with this piece of junk safety latch.

I followed the directions in the owners manual on how to release a stuck secondary latch several times but of coarse that didn't work.

Here's how I got it to release...

I used the jack placed to the side to push and hold the wheel up against frame allowing the retaining mechanism to dangle (so you can work on it).

There was enough room to get a screwdriver (or whatever you have that will fit up there to pry with) between the collar and latch to work the latch free.  See picture for correct side to pry on...when you're crawling under the vehicle you will be able to only see the very bottom of latch...one side has a notch and the other side doesn't...pry on the side that doesn't have the notch as this is the side that has the catch.  By prying on latch arm and pushing alternately on the release button (button at bottom where cable comes through) I was able to free the corroded/dirty latch.  BTW...when I got home I checked to see if my son's pickup spare could be lowered and his was stuck too so we did the same procedure to release his.

Pictures are of latch after I got it released...ONLY use for reference for which side to pry on.  We decided to cut the catch hook off with an angle grinder so we don't ever have this problem again.  DON'T do this as this defeats the safety feature...either clean and lube or replace with a new ratchet/safety lock system.