[davepl]

I wonder if you have a short somewhere, or a cross in a circuit where your lighter or dome lamps or something always hot is spliced into the IGN circuit?

I would have guessed the switch too, but if it's disconnected, not that...

You could try popping fuses out of other circuits and see if that removes power to the IGN lug, at which point you'd know what circuit is crossed (if one is).