All lights suddenly failed

[pmansson]

on my rev counter. The other instruments remain fully lit.
What might be the issue here, anyone....?

 

[61porsche]

One of the two lights has lost it's ground since the positive wire ( grey/ blue) continues on for the remaining instrument lights,clock, etc. Or one or both of the bulbs ( lamps) are burnt out. A piece of wire grounded and touched to the back of the tach would be one way to test.