An option: I did an emergency fix on son's 81 when he reported the failed OD wire/switch syndrome (2nd episode of this) while away at college. My next visit to him, I packed a late 240 rear demister switch, which is a momentary contact type, a made-up wiring pigtail of two wires connected to that switch, and on the other end the proper male (IIRC) connector to mate with the connector that takes the OD shift knob switch wires from under the carpeting on the passenger side up to the OD relay.

This was pretty easy to fish through, and install the demister switch in a blank spot on the console. Unplugged the shift knob harness from the under-carpet connector and plugged in the new wires. Immediately back to a working OD with switch wires that never move, chafe, or disconnect. This was to be a temporary fix, but after three years he has no urge to change it, and can easily prod the new switch without looking.

(To provide an OD switch backup for my own 83, I replaced the original sedan wiper lever with one from a wagon, and use its rear washer switch (momentary contact) with wiring spliced to the original wiring to the relay, to provide a redundant OD switch. If the gearknob setup breaks or shorts out, I can just unplug it at the connector mentioned above. Not my own idea - saw it here years ago from one of the BB gurus.)