The ball trough has the mechanical switches .
The wiring harness looks good. I have made some more progress.
I checked every switch again in single switch test looking for any others that were cycling between open and closed when held closed for a while (same behaviour as rh trough has) and found all but two of the switches in the same row are . (I thought I had already done this check )
I then measured across the NC contacts of all these switches and found most were reading open. I reflowed the NC and common contacts of these switches and this has improved the fault situation a lot .
It is still there but the open/close frequency is a lot less now to the point where I can start and play a game but sometimes game halts before serving next ball and/or occassionally does a ball search . If the trough switch wasn't affected I doubt anyone would normally notice this fault .

I don't understand how a bad solder joint on the NC side of a switch can affect the NO side of the switch (other than if the bad joint is on the common terminal I guess). These switches were still passing self test and registering closed (just toggling between open/closed when held closed) .. but if you just closed them as long as a ball would then they registered closed ie .. work normallly in game play because only the trough switches and ramp up/down are closed for long periods of time in a game (Opto's too of course but they are not part of this PITA fault)