1996 Isuzu Rodeo

Hello. I have been having a lot of
electrical issues with my 96 Rodeo.
At first it was just being
temperamental with the door and
dome lights, whenever I would open
my doors sometimes the lights
would come on and sometimes they
wouldn't. Then, later on, I noticed
that if I left my headlights on or keys
in the ignition while the car is off and
opened my door, the alert noise
letting me know that my headlights
were still on or keys still in the
ignition would sometimes work,
sometimes not. Then things on my
dash and stereo started happening.
Not all my dash lights work, havnt
worked since ive owned the car. The
gauge lights don't work, but my
indicator lights work. One night i
went to leave work and when I
turned on my headlights, my stereo
shut of for a second then turned
back on, my dash lights also
flickered. This same thing happens
when I turn on my high beams or use
my blinkers as well. But what's even
more strange is that all of my lights
on my dash shut off or turn back on
when pressing the breaks.. The
stereo shuts off for a second as well
as the headlights dim for a second
when pressing the breaks also. I can
be parked with the car running and
each time I press my breaks
everything shuts on or off, and if I
have my heater on I can hear it lose
a bit of power then go back to
normal when stepping on the breaks.  
My heater also loses power when
using my blinkers. I can hear the
heater losing power in the same
intervals as my blinker, then it goes
back to normal once My blinkers off.
All of this is very temperamental as
well. Some days it does it, some
days its fine. Or in the morning it
does it, then later on in the day it's
fine. I'm not sure what would cause
the breaks to interfere with
headlights/dash
lights/stereo/heater.