OK I'm gonna waste my time & try to explain this... Your headlights, turn signals, parking lights & dash lights are all fed by the same overloaded wire... When ever your headlights are on they aren't as bright as you'd like because they don't receive as much power as they would like.... Add the drain of turn signals & the headlights get even less power so they dim, the dash lights dim, the heater blower slows down (also fed by the same overloaded wire) All these loads cause the bulkhead connector to overheat which just amplifies the problem.......

Solution Add relays to feed the higher powered circuits such as high & low beam head lights & the blower motor.... Now these items work properly because they receive a dedicated power source, the previously over loaded bulkhead connector suddenly doesn't carry more than a few amps & all the minor loads receive full voltage causing them to work better too...

Oh BTW If you have more options like power windows or a power top on your car the original problem is worse but the solution is still relatively simple & even more effective....