Hi TH,
I am a little confused. Will it crank using the key-switch? Although you seem to indicate it will, the rest of your post seems to indicate the opposite. Will the car start with the key in the run position and starter activated by the solenoid button?
If the ignition key does not trigger the starter and all other switched-power components function (unit only work with ignition on i.e. wipers, etc.), then you are getting power to the switch. If you receive 12v at the solenoid with the ignition switch at start, your ignition switch is OK and the solenoid is at question. If no power is present at the solenoid when the key is at start, the line or switch is bad.
If no switched power components are functioning (or 12v is not present at the white wires connected to the fuse block), with the key in the run position, your switch is defective or is not being fed power from the regulator. If no power is at the switch, I would check the brown wire connections at the switch and regulator.
Based upon my experiences, I would check connections at the solenoid and regulator first.
All the best,
Ray 64BJ8P1