Thanks. Definitely nothing wrong with it. I'm going to take the dash out and trace everything back. It's a rebuilt rally car. I suspect the excite wire is maybe broken somewhere or a loss somewhere in the ignition circuit. All earths seem good. It's pretty simple wiring I reckon - a big kill switch on the dash (new one ordered) and a Start button. Twin fuel pumps whirring away nicely.

Problems after rebuild were: Volt meter reading low on fire up then at some point down the road it would jump to 14V at random. It's never revved past 5K without a loud bang and going into limp mode. Made doubly bad as I have a paddle clutch that needs run-in and I can't use proper boost. Arggh!!