I use the ignition key.  The internal lever needs to be fixed.  That is
a safety item.  Here are a few old posts:

"I've seen something similar once.  Removing the mechanism showed that
the rivets holding the two halves of the lock together had loosened up.
Banging them a few times with a hammer and heavy punch tightened the
rivets and restored proper function.  I hope this works for you."
Mike F. Thornhill (near Toronto), Ont.

"My tailgate lock was dodgy when I got it. Couldn't unlock it
electrically, and could only sometimes unlock it with the key. The
electric device made sounds, just didn't unlock the door. I pulled the
upholstered panel off and found this inside:
http://blizzard.zmm.com/volvolock.jpg  
The problem was that rod going toward the top left corner. It threads
into the white piece in the middle and just needed to be adjusted a bit
to keep the other parts from jamming. I don't remember the exact
operation of the thing any more; it took a little examining at the time
to figure out which piece was supposed to do what, but it wasn't rocket
surgery."
Ernest Scribbler