2008 DTS. What could be w Instrument cluster goes to zero Occurs while braking

The "clicking behind instrument panel" sounds like the biggest clue -- I'd focus my attention on determining what is causing the clicking noise and tracing back from there. A diagnostic tool is extremely helpful at checking both body "B" and chassis "C" diagnostic trouble codes. This can possibly help point you in the right direction also. www.repairpal.com/repair-shops