If the diamond isn't powered that would be my first guess. Second guess would be loss of common rail and the opposite side wheels being on plastic or insulated parts. What is the pick-up roller center to center distances on these engines? ? The fact that all of them stop seems to be the crossover wiring,
It will most likely be an easy fix. You could also show in a sketch what rails have wires hooked to them and where the outers are connected.
