Sounds like the problem is the entire IGN side of the key switch is dead. There is really no need to perform the system relay pin test because we already can guess what the results will be. The results will probably be zero volts also.
Something doesn't make any sense here. We have to back up for a second to an earlier step. In entry point 1 of this thread you said "no power on ignition side of switch,but accessories side is good!". In entry point # 5 you backed up that statement.
The Accessory side of the ignition switch supplies voltage to the brake light circuit. If the accessory side is really good, you should be able to place the key in accessory, apply brakes and see the brake light come on BRIGHT... If you can,,,, then once again go back and group all three wires at the ignition switch, press on the brake pedal and check to see if the brake lights still come on BRIGHT.
I have this feeling the answer will be No. The brake light will not be bright. But if the answer to this is YES, (the brake light comes on bright while the ignition switch is grouped),, then I want you to => group all three wires at the ignition switch, press on the brake switch and while you see a BRIGHT brake light,, take your volt meter and check to see if you have 12 volts on BOTH sides of the IGN,,INSTR,,& LIGHTS fuses. (3 fuses)
I will almost bet the answer to this test will be "no". That is, with the ignition switch wires grouped and brake light glowing bright, you won't read 12 volts on BOTH sides of those three fuses OR the brake light will no longer be glowing bright. Something will have to be missing...
I am going to take a wild guess and say the brake light will no longer glow bright when you group all three ignition wires together. And the voltage you read at those 3 fuses will be something like 2-3 volts (while applying brakes). That would make the most sense of all possibilities.