Mitsubishi: 99 Montero Sport Power Lock trouble

My wife has a 99 Montero Sport XLS. Recently her power door locks have
stopped working on a regular basis. They work sometimes, they don't work
others. It doesn't matter if she's using the alarm remote or the buttons on
the door itself. The fuse in the driver's side panel is fine.
I haven't worked with power door locks before so don't really know how the
system really works.
Anyone with any ideas or who've had this before and found the fix?

My wife has a 99 Montero Sport XLS. Recently her power door locks have
stopped working on a regular basis. They work sometimes, they don't work
others. It doesn't matter if she's using the alarm remote or the buttons on
the door itself. The fuse in the driver's side panel is fine.
I haven't worked with power door locks before so don't really know how the
system works.
Anyone with any ideas or who've had this before and found the fix? I've
submitted this a couple of times and gotten no response - please let me know
even if it's not a "home fixer" or if I'm just SOL altogether.