When in doubt you should always use a multimeter to find out what your electrics are doing or how they are wired or how they should be wired.
Wire colours are merely a rough guide if you do not know what changes a previous owner made.
If you need to trace the connections to the ignition switch take it out. First disconnect the battery, remove the panel knee trim, carefully unscrew the retaining ring nut and push the switch back through the panel and then hopefully there will be enough slak in the wires to ease out into the knee area where you can get at the contacts.
Connect the battery for a while to use a voltmeter setting find which is the always live terminal (Live when switch is in the OFF position).
On the ignition switch one wire is always live 12v coming from the battery.
Once you know which terminal (lets call it the Supply terminal), disconnect the battery again and use the ohmmeter setting to trace switch actions.
Put one probe of your ohmeter on the supply terminal and use the other probe to determine which other contacts it is connected to for the various switch positions (Aux, Off, Run, Start)
Aux position is twist the key anti-clockwise (it stays there).
Off position is usually with the key vertical
Run position is twist the key clockwise one click (it stays there)
Start position is twist clockwise from the Run position, it is spring loaded to return to the run position when you release twisting the key.
The permanently live contact should have a Brown/blue wire on it
The Aux contact (which should go via a wire which should be white) to the fuse box, is connected in all positions of the key except OFF
and STARTThe Run contact is connected only in the run position AND IN THE START POSITION. It should be connected to a white wire thart goes to the ignition coil. It may (probably) go there via the tachometer sensing loop.
The Start contact is connected only in the START position. It goes to the starter solenoid activate terminal via a wire that should be Brown/Yellow
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On my old starter switch (which is no longer in the car) the contacts are not identified by letters or numbers. It is I think a Lucas one. Its type number is 31953H
Viewed from the back near the bottom is a SINGLE-connector contact which is the START contact then going clockwise there is a DOUBLE-connector contact which is the Aux contact, then
continuing clockwise there is a DOUBLE-connector contact which is the SUPPLY contact then
continuing clockwise there is a DOUBLE-connector contact which is the Run contact.
Image from Holden website
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edited: add
and START to the Aux contact non-connection