Towing a trailer with electric brakes- you should NOT have it wired to the brake light circuit!! If you have an under-dash or under-steering-column controller, it uses inertia to apply the right amount of brakes, and has its own power source.
Regular braking/late light: on our vintage XJs the brake light switch is that funny thing clipped onto the end of the brake rod at the pedal. I bought a later-model switch (6 wires come out of it, three circuits, some on, some off with pedal out) to replace mine for use with a double diaphragm booster. It looks like it will fit into the bracket above the light switch, which holds the cruise cut-off switch. Find a pair of wires that are on and off with the pedal in or out that are the same logic as the oem switch, and use the bracket with the new switch to replace both the brake and cruise switches, and the third circuit as well (whatever it is). I got my replacements (two, actually) from a newer jeep and a chrysler car in a u-pull wrecker. 4xBob