PTU Wiring

Having had problems with the zed blowing PTUs I've come to the conclusion that a bodged wiring loom is at fault (taped wires everywhere) and I inteded to bypass the loom between the PTU output connector and the coilpacks to avoid the 4 volt backfeed I've been getting blowing my latest PTU. After studying the wiring diagram I saw that the PTU output connector wires, according to the diagram, go straight to the coilpacks but I have found this not to be the case on my car. The output connector wires infact go back into the ECU. Does anyone on here know why they go back to the ECU? What happens to the PTU output signal inside the ECU? I've realised that it could mean that not only is it a new 'engine bay wiring loom' I require but also a new ECU because that could be what's causing the backfeed.

Cheers,

Vern