What was found
PILOT TAXIED OUT TO RUN UP AREA & RETURNED WHEN GMU-700 FAIL WARNING CAME UP ON ALERTS, CAS MSG SYSTEM. G1000 SYS INSTALLED. UPON INVESTIGATING BY THE AVIONICS SHOP IT WAS DETERMINED THAT THE POWER WIRE TO THE GMU-710 UNIT INSTALLED, FLIGHT DIRECTOR, YAW DAMPER & AUTO PILOT HEAD, HAD CHAFED THROUGH THE WIRE & WAS SHORTED OUT TO THE TOP OF THE AVIONICS RACK BEHIND THE MFD SCREEN. NO BREAKERS WHERE FOUND POPPED. REPAIRED BROKEN & SHORTED WIRE. PERFORMED OPERATIONAL CHECK OF ALL SYS & FOUND OK.