The car: 1997 Sable GS.
I fixed the MF switch as per the excellent instructions elsewhere in this site. The process is clear and straightforward.
When I put the whole thing together and I tested it, in the second intermittent position from lower to higher speed, the wipers work continuously like if they were in "LO" and not in the second intermittent setting. The rest of the settings work fine.
Where did I mess up?
1997 Mercury Sable GS, 3.0 Duratec, AX4N transmission