Matt,
  The power lock system is fairly primative -- the actuators (actual
"power lock": a box consisting of an electric motor, a worm gear, and a
big switch) are connected to the lock button itself, not to the lock
cylinder.  If you've got the space to do it, pop off the door panel on
the offending side and have a look around, you'll see how the actuator
sits in the door and how the mechanism works.

  A couple of things might be going on, including a break in the wiring
harness as you speculated.  IIRC, the harness consists of three wires,
and some kind soul in the archives has laid out the voltage you would
expect to see running across each pin.  Grab a multimeter and have a
look.

  Alternatively, what might be going on is that the actuator itself on the
offending side has gotten water into it, and is so corroded that the big
slider switch inside isn't making useful contact anymore.  You could: a)
open up the actuator itself on your workbench / kitchen table, clean it
out, and rehab the switch, or b) drop $70 on a new one from one of the
vendors.  Having tried the rehab route first (I'm a starving student), I
found that my driver's side actuator was so crapped up inside that the
motor was rusted.  Bit the bullet, bought the new actuator, problem
solved.

  Let us know how it goes.

Best,
d.
1990 GL -- "Mudskipper"