Toyota Repair: Toyota Tercel 1997 2dr., toyota tercel, amp radio

Question
Hello.  This crazy little problem developed today while I was trying to install a  
CD/radio unit in my wife's Tercel.  The previous radio had been stolen  but no
apparent damage had been done to the car or dashboard.  I secured a used
replacement unit and spliced together a radio to wire-harness adapter using
a
wire color conversion chart I found online.  Everything connected together
right
and looked good, but the receiver didn't light up when I turned the key.  I
even
started the car to be sure power was available but still nothing.  Then I found
the
15 amp radio/lighter fuse was blown, though how long it had been like that I
didn't know.  Lacking a replacement fuse and trying to be smart, I removed
the
15 amp taillight fuse and put it in the radio fuse slot.  Now, the radio still did
not
work and in addition the shift lever would not move from Park and the car
would
not start again.  I disconnected the radio and returned the taillight fuse to it's
slot, but there was no improvement.  The battery checked out with 12 volts
but
the electrical system was acting half dead.  When it started getting dark I
noticed
the dome light dimmed when I pushed the break pedal and the taillights did
not
come on.  Online I found mentions of a brake, taillight, shift lever interlink
system which seemed relevant but not real helpful.  Then someone talked
about
a shift lever override button and this was great because using it I was at least
able to move the Tercel out of the driveway where it had been stuck, blocking
in
our other vehicle.  Obviously, there's some type of short happening but
where?  I
put a new fuse in the radio slot and it hasn't blown again.  All the other fuses,
including those in the engine compartment look OK too.  What do you think?

Answer
The first thing is to check to make sure the battery is good, is it charged and have at least 12 volts? The dome light dimming when the brake applied would indicate a discharged battery or loose connection at the battery. Do the dash lights come on with the key? Does the engine start? Do the headlights turn on? Try disconnecting the radio completely and see if the car returns back to normal being sure all the fuses are OK, if so then there is something wrong with the wiring to the radio, maybe a hot wire grounded causing a short.