Why my headlights cause my car to lose power?

So I’ve had some electrical problems with my car
and if I let it sit and get into it, it starts up fine but
when I go to turn on my headlights I lose power to
my dash my locks, rear defrost like some stuff
works some doesn’t and when I go to park it locks
it self in park so I know that I probably have a sort
somewhere but I wanted to see if anyone on here
could maybe help me locate it easier I’m lost atm
so any help will be appreciated thank you