with the stalk in neutral there should be continuity between the white "in" wire which comes from the brake light switch to the 2 "out" wires to the dr/pass brake lights (which are the same filaments in the 1157 bulbs as the TS filaments). this is when you hit the brake (& stalk in neutral) the 2 rear brake light circuits light up). with the stalk up or down one of those out circuits is redirected by the TS harness to the flasher which ain't telling you much as I am rusty on diagnosing further on that. might be a loose connection in the TS switch harness & it'd be good to confirm/elim that area as a start