Don't overthink this, troops.
The fix is practically free, and uses nothing but a soldering iron and some tape.
1...unscrew the Bendix connector off the back of the light switch.
2...Unwrap the tape back a bit, about 3 or 4 inches.
3... sort out wires #491 and #21.
4...Pull wire 491 away from the others, and cut it close to the connector. Tape up the short end.
5...Strip 1" of insulation from wire 21, back 4" from the connector (but DON"T CUT THIS WIRE). Be careful not to damage the wire strands.
6...Strip 1" of insulation from the long end of wire 491, wrap it around the bared spot on wire 21.
7...Solder the connection, wrap it with tape, and retape the entire loom as original.
8...Reconnect the connector to the light switch, you're done.
Parking lights will come on any time any Service Drive (includes headlights) switch position is turned on.
Parking lights operate as usual. Beats spending a C-note on that gizmo...
For the uneducated, the light switch is designed to inhibit visible lighting from coming on without a conscious effort in order not to give your position away at night. The only unlocked function is the blackout markers.
DG