Left side brake woes

I think redfish's guidance is good.

But if you want to read how it works, here's the master tech explanation of the turn signals & stop circuit.
Hazzards is on page 7.
1967 Chrysler Imperial Electrical Accessory Circuit From the Master Technicians Service Conference Session 236
and the filmstrip if you want
1967 Electrical Accessory Circuits Movie from the Master Technician Service Conference Series (Session 236)