My 72 Demon brake light and both rear left and right turn light don't work

I assume you have a service manual. Check for power on both sides of the fuse(s)

Second place I'd access is either the column switch connector for the TS switch, or else pull the left kick panel and access the rear harness connector. Get a light/ meter and check for power

Look up near the start of the electrical wiring diagrams in your service manual, there is a list of what fuses serve which loads.

Keep in the back of your mind the path. Path for brake light switch is "always hot" fuse, through the brake switch, to the column TS switch, and through it, and out to the various TS lamps

Path for the TS is power through key, fuse, flasher, to TS switch, and off to 4 corners

DO THE hazard flashers work? They are a separate flasher