01 Ford Explorer Sport Door Lock won't unlock... sometimes

My 2001 Explorer Sport has developed a problem with the drivers side door lock. When I put the key in and turn it OR when I use the remote to unlock, you can hear the mechanism try to unlock, but it doesn’t… about 80% of the time. So, I find myself unlocking the passenger door and reaching through to unlock this. Before I try to fix this myself, I thought maybe someone might have some thoughts on the cause. Thanks!

The solenoid for the lock seems to be sticking or there is a wire connection problem going to it and it isn’t getting the full voltage it needs to work correctly. You are going to have to get in the door and see what is going on.