I've spent a bit of time checking the wiring, the blue wire has continuity all the way to the ecu, but still unsure where the grey wire goes yet. The red wire is showing 13.8v (unplugged) when engine running which i'm told is correct. I've even swapped the ecu for a spare one i have and it does exactly the same thing.

I'm going to swap out the alternator this week to see if its that, i can't really see what else it can be apart from the grey wire. My money is on the alternator being goosed due to the jump start. I've read these smartcharge systems can spike upto 18v when jump starting. We'll soon know...

Cheers for your help so far

Ed