I have needed to sort this out for years!
Using the wires supplied with the layout that electrically join the two baseboards, I spliced in a phono plug.
With it all plugged together this is what it looks like. Certainly a lot more robust and worthy of its job than my previous effort!
The greta thing is that I can now make a similar set up for Chalkdon my 009 narrow gauge layout where this controller will also be used. All I need to do is unplug the USA switching layout wires and move the controller over to Chalkdon. No more twisting wires together or using various clamps to try to make electricity flow!