Brake light problem

Switch on master spring mechanical or fluid pressure?
a. Either way, remove the wires off the switch, ohmmeter shows and on/off read at the meter?
b. Liquid switch can on/off as well?
c. Keep wires off switch.

Wire off master is the one probe clamped to the one wire from the switch.
a. Find the wire to the brake light connector, closest to the switch.
b. That would be found off the switch harness leading to the headlight bucket?
c, Note the second wire from the switch out of the switch's harness to the main harness.

Pin' male/female ends not making contact. Wires have an open in the switch harness?
a. This would show it by the ohmmeter set to infinity.
b. So that's one section from end to end is the switch harness tied in with the starter, lights, etc.
c. Then main harness wires to the next disconnect; leading closer to the taillight/brake light harness .

Did you change anything?

If you did I would think it would be the microswitch. Some of them run open circuit vs closed circuit when pressed and that might be the issue.