I have no experience with motor vehicles or motor vehicle electrics - but that does not stop me offering an opinion...
It's probably like this...
The dashboard does not illuminate until the ignition is turned on - the ignition switch will not be able to deliver the power so it energises a relay. 
If the relay that supplies the dashboard is defective there will be no lights on the dashboard.
Of course - I could be wrong.
                
 Good Luck...
                
 November 2015