[Warning Light] Dials fall after 15 seconds

[Robawcock01]

Hi guys just wondering if anyone can help I have a 2003 1.9 diesel berlingo and once you start the van all ok but after approx 15 seconds all the dials drop and have to restart the van for them to work again but happens again and again I have carried out the Bsi reset but no luck, and checked the earths all seem ok don't really want to spend £££ on parts without checking anything first thanks in advance rob