unable to unplug 12 volts at fuse box

I frequently need to remove 12 volts from car. Going into the trunk is a hastle. I cannot unplug the 12 volt connector at the fuse box. There is a locking tab that I have flexed both directions while pulling the cable with pliers, but the cable will not come out. Which direction do I need to push it? Is there a trick to removing the

cable? Is a special tool required? see pics

 

After thinking about, the tab probably pushes in toward the cable. I tried using a screwdriver (shown) and an icepick. I pshed them deep. I have wiggled the connector around while doing that and pulling with pliers. The previous owner might have had the same problem. Maybe he did not lock it in for future use. It left me stranded recently until I pushed it in tight and it locked.

 

I finally got it unplugged. I used a knife blade to slide between the plug and receptacle on the locking side. But, I think that the connector was not locked, but stuck. In other words, the locking tab was not the problem. I had to pull hard to get it out. Now, when I push the plug in part-way, it gets real tight and does not pull out or push in easily. I don't know why. Maybe the plug (or receptacle) is distorted so that it is a sqeeze when inserted. Maybe I will sand it or lube it with a dry lube such as teflon or vasoline. I doubt that the metal contact is the issue.
Thanks for your help and suggestions.

 

I applied some 3-M silicone paste to all 4 sides of the plug. That helped, but was still a little tight when pushing plug in fully. Then, I applied dielectric grease to the slot where the electrical contact is. Now, it is smooth and easy.