I went through a long drawn out affair this spring with our 2001. I did most of the things you did including the brake switch, servo, left hand switch on the column and finally, the ECM. Each time I tried something, I had myself convinced that that particular part was the problem. In my case, the light was always on and nothing I tried would make it go off but the system never worked either.
This was undoubtedly not related but it started working after I changed the fluid and filter in the transmission.