Speaking to a couple of people, I'm going to circumvent what seems to be a dodgy fuse box or wiring connection for the ECU power feed, and run a second fused relay in the engine bay, basically mirroring the relay for the charge cooler pump.
This will be run direct from the starter positive feed (got solid battery voltage here) to a relay triggered by the starter relay (as per CC pump).
This should hopefully give good ECU voltage, and at least rule this out...
