[Alan Roehrich]

I do not advise putting external switches on a transmission, if not absolutely necessary, as it is a place for a leak. A leak that could put fluid on the track, getting you a fine, possibly a wrecked car, and even a fire, should the switch fail and create a real leak.

Yes, I suppose it is possible to use a pressure switch on a line pressure tap to do what you want, but I wouldn't do it, and we do not do that on either car. A switch on the shifter is the correct way to do it.