1989iroc-z5.7

I have 89 iroc 8.7 that i am restoring, After i had the car running good i decided to get into the interior everything was fine till i got to the heater control above the radio were i replaced the blown out bulb and everything went out no headlights fog lights,horn,power trunk,power door locks,radio, dash lights or interior lights I checked all the fuses they are good i replaced the relay next to the master cylinder, still nothing. i verified fuse line after the starter they are good. however when i check the accessory fuse panel with a probe it gives me ground and i send 12 volts in the same line the lights turn on what can be causing this problem, i verified all line tore dash apart all the wires are good. i apreciate any kind of help. Thanks, and if anyone is in tampa/Carrolwood and can come out and fix it i dont have a problem paying i just want it fixed.