Sounds like bad grounds at the turn signals and head lights. Can put an extra ground from the engine block to the fire wall body sheet metal too to help with grounding of the interior and dash components.
When you have dim lights or other lights in the system coming on when you don't want them on, that is bad grounds.
When you have bad grounds the electricity is looking for an alternative path to get back to the battery, back feeding through the other lights and components.
50 year old cars here, connections and grounds get corroded.
You can go around with the light switch on and feel the connections (even at the firewall junction block), back of the headlight switch etc. If you find a connection that is hot not making good contact, then that is part of the problem.
Electricity follows the path of least resistance.
