engine won't start

Something is up with the ignition switch. The part of the switch that feeds the starter solenoid also feeds the rest of the ignition circuit. Start there. Take a meter and figure out what wire is hot all the time. Then poke around and find out which wires go hot when the switch is turned on, then find the wires that go hot when turned to the start position. This is for a slightly different GM vehicle, but on the ignition switch, Gm has used the same color code for years. The rest of the schematic may or may not be accurate, but it should get you close enough to figure it out.