No, my question was "how did it start" or in other words perhaps, can you say it was working, you know what it is supposed to do, and suddenly last week it stopped?

I wonder if you know what it does (it locks out 4th gear) or if it ever worked for you in this car. You could have just acquired the car and the PO had the hydraulic circuit bypassed. You could expect it to do something it won't; for example I can drive up my street and operate the switch on my perfectly working car and not sense any "gear change" because I've not attained the speed the governor needs to see to engage overdrive. The switch disables overdrive.

Once you establish that it worked once and now it doesn't, you can begin a troubleshooting procedure.
--
Art Benstein near Baltimore

Never put both feet in your mouth at the same time, because then you won't have a leg to stand on.