Problem resolved!
Christmas and New Year 'things' interrupted modelling a little, but on our first 2026 session, we cracked the wiring problem!
Going back to first principles again, we bolted the two boards together and traced every bit of wiring that was affected by the modification. This time we found an anomaly relating to the extra wire running between the boards, through the loom. The loom on one board has two plugs and the new wire had been soldered into the wrong plug!!! (No excuses, but both plugs had the same spare pin, which clouded the issue). It was a simple job to move the wire to the correct plug. A comprehensive test was carried out, and everything worked correctly. A great moment! We now need to wire-up the new rotary switch that will replace the four switches to control the four points.
