Jumping the red wire to the white wire into the column switch will make blink both rears with turning switch in rest position. That will discard the flasher of course, but not the turning switch completelly. On rest position turning switch gets rear lights linked to the white wire which is the normally closed position for the brake lights coming from pedal switch

then as mentioned on article, feeding each corner ( both greens, tan and brown ) and get the lights work but not through the switch which will confirm switch is bad.