For anyone who's interested, new switches are sold only as a pair
complete with wiring harness. . .around $70, but Internet discount
sourcing around $40. OEM Ford Motorcraft only. Replacing the switches
is fast and easy, but not so for the wiring harness, so I didn't even
try -- left the original in place and used it to connect the new
switches.

First, disconnect the battery to prevent the airbags from accidentally
deploying during removal and when attaching connectors. Wait five
minutes after disconnecting the battery before removing airbag, as
there may be backup power to it. May not be necessary, but easy here to
error on side of caution by just removing battery's negative connector.
(If your radio's preset stations are important make a note of them
before battery disconnect in order to easily reprogram.)

Airbag is bolted to the steering wheel by two 8mm bolts on either side
of the column just below steering wheel -- pop off the round plastic
flush covers to reveal the bolt heads. After removing both bolts, tilt
out the airbag, disconnect its wiring harness plug and set the bag
aside. Each switch is connected by two screws. After removing them,
lift out the switch and gently pull the connector plug. Do not even
think about touching the wires to pull the plugs. . .they'll dislodge
from their tiny crimp contacts. Instead pry the plug out, working
progressively along the mating edge with a small screwdriver. Same
prying for the new switches which come with harness plugged in, just in
case you ever have a need for the new harness.

The remainder of the job and reassembly is obvious.