Electrical wiring - bomb disposal

Electrical wiring - bomb disposal - do I cut the blue wire or the red??????

It's blooming nervewreckingly complicated without a wiring diagram. 

The car has an ECU, which needs to remain, and an immobilizer, which seems to need to remain.

But surely all this spaghetti is superfluous? 

I'll keep on cutting until the car stops then rejoin if necessary.