88 Firebird- no start-HELP!

My 88 Firebird (with 250,000 mi) 305 TBI, Engine was rebuilt @ about 200,000 was running OK. Started to run rough like a wet distributor. So new cap, rotor, wires etc. Went in- got alittle better. Then, it was a dark and stormy night driving along and BAM! Everything electrical went dead! No lights, no engine, no wipers, nothing. The only thing that did work, was the horn which hasn't worked in three years. It went off & I had to physically disconnect the wires to turn it off. I've tried a new battery but nothing changes. The dome light comes on, but nothing else. I'm thinking possibly ignition switch or neutral saftey switch. Ignition sw. Is REALLY worn out after this many miles & years. Anybody know how to test this? Or any other suggestions? Really love to drive this car, but right now it's a lawn ornament.