Bloody electronics, they've got no place in a workhorse!
I had a similar problem with a Renault once, and it turned out to be a crack in the PCB behind the dash that held all the relays and clever gizmos. Engine vibration would sometimes cause the crack to open, shutting off everything that ran across where the crack was and making the dash flash and flicker like a Christmas Tree. Fixed it with some solder - but with modern cars that's probably far too crude.
(*sigh* that's why I love my leaky Land Rover!)