When I start my Ducato 2002 2.8D the gauges, clock and ODO go off. Once running they come back on. The battery is fully charged, any suggestions ?

It would be a wiring issue with the ignition switch. But just what, I don't know.

I have the same problem with my 2003 2.5. Clock and ODO reset to zero when I start the engine. Must be voltage drop somewhere but as the voltmeter I've put in the circuit only shows a battery drop to about 10v as the engine turns over I can't see that causing it.
Anyone any possible ideas/solutions?