The brake light switch you're fighting with right now is only for the brake lights. You can see it in the below picture in the foreground. The brake light switch is black, with a brown electrical connector.
The cruise control vacuum dump (and TC lock up sensor) is the big white sensor in the back ground.
The bottom of the picture is pointing forward to the firewall, and the top of the picture pointing to the driver seat (click for giant size).
The idea here is that there is a plunger that sticks out of the white sensor towards the brake pedal assembly. You can barely see it in my picture. As you press the brake pedal, that plunger will extend. This controls TC lock up - at least it does in my MJ.
You can verify functionality by removing it and clipping a DMM to each of the terminals on the sensor and measuring for resistance as you depress the plunger. I don't recall which way the contacts are closed (I think it's when the plunger is all the way out). The recommended action is to go ahead and pop it apart and clean it up while you have it out; this sensor can get dirty/gunky sometimes anyways.
The white sensor has a plug with two wires, a black wire and a blue wire with an orange tracer. I assume the black wire is going to be a ground; someone will have to double check in an FSM.
Anyways, make sure that the plunger extends fully when the brake pedal is depressed and make sure it is fully unextended with the brake pedal in the normal height. You will have to do this with the truck running.
To check for TC lock up, you will tap the brake pedal while you are cruising at a constant speed (above 50mph, IIRC). You will notice a ~300 RPM spike and you should be able to hear the engine rev up a bit. With the TC never locked up, your trans will run hotter than normal; this is what was wrong with mine.
All of that being said, you may not have to adjust that white sensor. Just make sure it's working. Also, tighten the bolt that runs through your brake pedal sensor some more - I had to fidget with mine for a while to get the lights working correctly.