The brake/turn/flashers all use the same large filament in the dual filament 1157 bulb so there is (1) wire going rearward to the (1) filament on the pass side (& one for the DR side). I would seperate the dangling electrical connector for the brake/TS lights under the column & jump fire to the (1) wire for them. No go? then jump fire to that wire under the DR kick panel. No go? going rearward there's a connector or two under the carpet & same thing seperate/jump fire to check each one till you get fire/continuity to the rear pass socket & check that the bulb filament(s)is good. that the bulb base contact to the socket is good. On the ground side that the bulb case is making contact with the socket. that the socket (as said) has continuity to the frame. If all good (& you can shortcut that procedure as needed) then the problem is in the TS switch/harness because it is recieving fire from the brake pedal switch (the white hot in wire) and directing it to the DR brake large filament & it should be firing both sides at the same time (with the stalk in neutral)