dash cuts out for few seconds

Secondly, odd though it sounds there is a link between the bonnet open/closed switch and the dash.  It is used mainly for the strange arrangement whereby once the oil level light comes on, the bonnet must have been opened and closed for it to extinguish.  There is also the fact that the intermittent wipe will not work if the bonnet is open.  I would just check that the switch looks good and the two wires are not broken.

There is also a place on the wiring loom where it can rub on the top of the clutch pedal box which can cause the dash lights to flicker.

If you can get it diagnostics it might give you some clues.  It is important to have a complete scan so that all the individual controllers/ECU's on the van are checked.  The instruments controller and the Cent Elec controller AKA J519 are particularly important.

These are just some cheap and easy checks based on the most common problems but in reality there are many more possibilities.  Poor earths or a failing dash cluster could also do it for instance.  So really it is down to getting the multimeter out and starting with a simple check across the battery.  A fully charged battery should read at least 12.6v and between 13.7v and 14.5v (approx) with the engine idling.  If the regulator is faulty it may show as much as 15v plus.