[meric42]

Thanks all for your help, I think I've worked out the wiring situation. I think they use the standard horn wire with with a spring loaded center contact. The foam pad in the button appears to have deteriorated over time and lost it's flexibility. I am waiting for some high density foam to arrive so I can replace the original foam as this seems to be the only thing keeping the horn contacts apart inside the button. There doesn't appear to have been any spring internally like the other buttons or rings I am familiar with. I'll keep you all posted.