I have a 2007 ford fusion and i was driving one day and placed the seat belt behinf the headrest and now it is locked and there is not enough slack to move it. how do i get it unlocked ?

You remove the compressor and put a Bypass Pulley in its place. The routing and belt remain the same.

https://www.google.com/search?q=2007+Ford+Fusion+AC+bypass+pulley

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First off, are you able to move the seat forward, backward, or upward to free up the tension on the seat belt lock so you can again pull out slack? If not, are you able to raise or remove the headrest to create slack in the seatbelt and release the lock? Without a photo of the situation it's difficult to understand how you managed to get a seatbelt stuck around a headrest....

a standard ford head rest

look for a pusher button or pin on the base plastic where the two metal guides go into the top of the seat

might need to to push in both at the same time
and lift the head rest

if it stops at the top you keep pulling upwards

If you are able to feed the seat belt through the car seat, latch it then using the weight of your body and your knee in the seat push the car seat down and pull the seat belt out all the way until it stops. Once it starts reeling back in it will make a clicking sound letting you know it is locking. Feed all of the slack back into the reel and the seat will be locked into place.

Remove the cover over where the belt goes into, use a screwdriver to unjam the "cogs" thus releasing the belt. Replace the cover. That should fixya

Yes if you lift the headrest upwards it will raise and you may be able to lift it out, you may need to press a button on the seat top to do so.

haha we know you didnt do it on purpose, without seeing your problem and the hard to describe issue, i can only recommend to maybe try folding the seat to the cargo position, if that helps. if not, then you will more than likely need to disassemble the rear quarter panel, and unbolt the seat belt retractor from the body of the vehicle. sorry but there is no other way

I've removed the headrest on my mustang before. Some seats have a zipper or a way to snap the seat cover at the bottom rear. If you open it you can put your arm up the back of the seat. With the headresat down you can feel the locking piece that retracts when you lift the headrest. If you take a long shaft flat blade screwdriver and place it in between and lift up the headrest it will slide out. Yes, getting the screwdriver in place can be tricky but, it was the only way to remove the headrest without having the correct tool. I hope this can work on your vehicle as well.

Right below the headrest, there should be a little button like switch sticking out. Push it in and you can move your head down or up and off.

It is a safety latch that is doing it's job.

If you wreck the car the belt stops preventing you from hitting the dash or going through the windshield.

Try this test to make sure they work:
Get in the car and start it,

Put your foot on the brake, and put the seatbelt on -

Now yank on the shoulder part real hard if it doesn't stop immediatly you should get it replaced.