Finally got around to having a bit of a poke around in the ign on my Omega B that didn't want to start or turn off. Turns out the shaft that comes out of the ign barrel is snapped right in two would have thought the key itself would've been a weaker link. After chasing and reassembling a bunch of little springs and pins (which of course went everywhere despite my best efforts to remove the assembly carefully) I managed to hold the bits and pieces together to turn her over. So definitely just that breakage at fault and no other electrical bug-bears
So if anyone has an ignition barrel to fit a omega b, vectra b has the same one part#90512000, or knows of someone local (before I go asking offshore) who can supply one at reasonable cost I'd be happy to hear from you. Essential as it is to operation, I'm not prepared to pay the $95 I was quoted to obtain a used one from the wreckers on trademe (lwwlww).