Ok so my car is starting just fine

Ok so my car is starting just fine.

But the windows, sunroof, radio, A/C, blinkers, break lights, etc all are NOT working.
However, I was on my way to take it in and it all randomly worked properly again, and after that day though it is back to the electrics not working AT ALL.

We checked all of the fuses.
Tightened some wires.
Charged the battery.

It didn't help though.

At this point I feel like its a simple connection problem! Since it randomly was ok for a day.
But at this point I'm not even sure what to think or do and would love if it was something I myself could fix.

Thanks for the help!