OK so it took me a while to find the time to play. I buzzed it out and the white wire from the stalk that goes 0v when pass is pressed, goes into a black one in the loom which sits at 12v.
A bit of wire + a little solder and we have flashers again.
I didn't think these cars used relays in the lighting circuit but when I press the pass button, it's defo activating a relay.
Would this have been standard or do we think the PO installed it?
Ali K