There is a very common problem on '67 and '68 Cougars where the door just won’t open. The outside release button won’t work and the inside release lever won’t work. It doesn’t matter if it is locked or unlocked.
The good news is that by 1968, the engineers at Ford knew about the problem and published a fix in the service manual. Chances are if you are having this problem and looking for answers on the internet, you probably don’t have the manual. The first thing that I recommend to new Cougar owners is to buy a manual, as it is going to be the best money you ever spent, but you can do that AFTER we help you get the door open.
Since this is such a common problem, It has been discussed many times before. So many times that you end up posting things like this when the question gets asked:
You cannot remove the panel with the door closed without ruining the panel.
There is a procedure outlined in the factory service manual called the emergency unlock procedure. Get the manual. You will be instructed to bend a length of wire into a tool to unlock the door. This is a known problem.
Do exactly what it says in the manual. The door will unlock and you will save yourself the cost of the panel, and get a manual that you can really use.
Or you can destroy the panel. And then buy the manual, and make the tool and unlock the door.
I have copied much of this from a previous discussion. In that particular case a release spring was also out of position. This may or may not be apart of your problem but it is helpful to address that as well.
So here is the fix:
You need to make a tool from a piece of stiff wire to reach down inside the door to press the latching pawl down to release the latch. Here is a picture from the shop manual illustrating the use of the tool. The tool is about 20" long with a 1/2" right angle bend at the bottom and a 3" right angle at the top, to create a backwards S shape. I used an 1/8" diameter steel rod from Ace to make mine. The rod was stiff enough to require the use of a vice to help make the bends.
How this thing actually works.
The door locks on our cars do not actually lock the door. They disable our ability to unlock the door using the interior and exterior lever or button.
The door locks automatically as it is closed. There are two detents as the door closes, the second detent occurs when the door is fully closed.
The door is held in the locked position by a pawl, kind of like a tooth on a gear, that engages two recesses in latch. The pawl is held in position by the coil spring at the bottom of the latch. If this spring fails, the door will not stay closed.
The release mechanism acts to push down upon the pawl to push it out of engagement with the detent. The release mechanism is returned to position by the clock wound spring about its fulcrum. This is the spring that appears to be broken in the pictures.
When this spring fails, you will know it instantly because there will be very little resistance to the inside door handle or the outside push button. The lock knob will also be impossible to move more than a little bit up or down.
When the door is “locked” by the key or the inside lock knob, the release mechanism is actually rotated into a position where it cannot act to move the pawl. Unfortunately, there is a known design issue where the release mechanism can be driven up on top of the release pawl. When this happens, the door release and lock knobs will all appear to function more or less normally, but with no effect.
The problem is caused when the inside release lever is adjusted a little to tightly which leads to a pre load condition of the release mechanism. It is very common to have this problem after the door has been disassembled for glass replacement, or even an adjustment to eliminate rattles in the door, caused by the release rods.
In both cases, the door will not open from inside or out. The solution is to bend a long wire that can be used to push down on the release pawl. Once the door is opened the release rods can be adjusted accordingly.