2002 Buick Lesabre just died - electrical ?

Car was running fine since Jan when I bought it. 50K miles LeSabre Limited. It started normally then I released the park brake and it shut down. Horn honked once as it turned off.
Battery is 12.5 V, fuses all appear to be ok.( keep thinking it is a main fuse )
These things don't work: all dash/ speedo/gear shift lights, starter, ignition, wipers, turn signals, remote door key fob
these things work: trunk release button in car, door locks in car, 4 way flashers, dome lights, mirrors, brake lights, 2 seat memories working ok
ANY IDEAS BEFORE I TOW IT TO THE DEALER ???
thanks.guys
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Look for loose battery and ground connections, battery under rear seat. Then look for bad master fuses some under the hood some under the seat.

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I just finished doing that. I loosened and retightened the batt terminals under the seat then cleaned the positive post connectors at the front fuse box where the main pos cable comes in from the batt.
There is spark when the batt ground wire gets reattached under the seat and wrenched tight.
Weird thing. After I cleaned the front positive post and nut, and wrenched it back together under the hood, then I put the ground wire back on the battery terminal, the horn started and I had to pull the horn fuse to kill it.
After all that I still have no ignition lights or starter with all cables connected.. The horn will blast nonstop if I put the horn fuse back in.
???
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See if you have 12v going into the ign. switch, and 12v back out to the accessories in the on position. I believe the bcm controls a lot of these functions, make sure that is powered up.

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The horn is probably part of the antitheft system, try locking and un locking the drivers door with the key. This may turn the alarm off and reset the horn function.
Snow...

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Don't know about the rest but it sounds like your horn switch is jammed in the on position, or else somehow the horn is getting a hot connection despite the fact the switch is off. Time to get out the manual and the multi-meter.
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Well the problem was the remote starter/alarm someone added before I got the car. They had a single 15A circuit from my rear ign fuse supplying.......wait for it.......
30A+30A+15A+10A fuses under the dash in a rats nest of loose boxes, crap and wiring.
Idiots.
I had the GM dealer rip all the garbage out., cheap Taiwan boxes and heavy relays hanging down not even cable tied. It took him half the day to resplice and make good.
thanks for your help but I knew it was going to be a dogs b'fast as soon as I took the knee bolster off.
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Fusable link?

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