It was a special switch. Four terminal --when off, all 4 were isolated, when on, all 4 are connected together
You wire up a hazard flasher to constant hot power and feed that to one terminal of the switch
You connect one switch terminal and branch into the brake like switch output (to the TS switch)
You connect one terminal to the front left signal lamp wire
You connect the last terminal to the front right signal lamp were
So "when on" the lamp connects flasher output to the brake line going into the TS switch and to the left and the right front lamps.
You used to be able to buy "add on" hazard switches which usually were unitized with a flasher attached
