With these cars getting older, some creature comfort and luxury features are starting to wear out. Nowhere is this more evident than with the power door locks. One day they work fine, the next they might stop altogether. This section will help you to troubleshoot the power door locks.
Really, power door locks in our cars run from a pretty simple system. Power from the fuse box is fed through relays (behind the dash on 1983-86 cars, underneath the passenger seat on 1987-88 cars), which is then fed to the switches on either door panel. From there the power is fed to the door lock actuators which are buried inside the door, behind the door panels. Here are some basic procedures for tracking down the problem:
If a switch or relay change does not solve the problem, you will pretty much have no choice but to remove the door panel and at least test the stock power door lock actuator. The actuator is usually a goldish or silver color with a rubber boot, and is attached to a bracket that is pop-riveted onto the door frame. The hook end of the actuator loops through the door latch mechanism. It's a pretty tight reach into the area so be careful (and also remember to put your window up first!).
Your first instinct may be to just punch out the pop rivet to remove the actuator, and that's fine. Upon reinstallation you'll need to use a bolt, nut and some washers (or another large pop rivet, if you have access to one). However, Jason has passed along this alternate method of removing the actuator: Reach your arm inside the door and grab hold of the actuator. There is a bracket that holds the actuator (you know the one, most of you drilled the rivet to remove it). The actuator has two pins that hold it to the bracket. Twist it, one of the pins will come out of the bracket. Then pop the other side out.
Now that it's out of the bracket, unhook it from the door latch. The wiring harness simply pulls off from the bottom. Once the hook is off the latch mechanism (just be patient), you can fully remove the actuator from the door. To test it, get the harness from inside the door and plug it back into the actuator. Use your power door lock switch to see if the rod does indeed move up and down. If not, or if you have sporadic success, then you will definitely need to get another actuator.
About that new actuator: if you're thinking about taking a trip to the Ford dealer to order a new one, you won't find it listed for a Cougar or Thunderbird. At last check it was available for a Lincoln Mark VII, though. Or you can use a Mustang actuator. Basically most Ford vehicles used the same actuator. The only thing that differs is the rod, with both its length and its end configuration. Some rods have an "S" shape, and some have a "J"-shaped hook. It really all depends on the options your car has (keyless entry, illuminated entry, etc.) as to which type of rod is used. The main goal is to try get a replacement actuator with the same type of rod already installed; however, you can use any actuator and just switch over your rod, if you so wish. There is a keeper lock with ball bearings inside that can be removed to allow rod swapping. It is a little tricky but can be done if you're patient.
There are some companies, such as A1 Electric, that offer door lock actuator kits with lots of different rod types in the same kit, so that you can create exactly what you need. These kits are probably available on eBay or Amazon as well.
You can always get a used actuator from the boneyard, and that's okay. Just be aware that you may end up with a bad one, or one that will go bad perhaps sooner than later.
Before you install your new or used door lock actuator, lift up the rubber boot and apply some white lithium grease. This will keep it lubricated for a long time and keep water from infiltrating the mechanism.