NORTH AMERICAN B25 CREW LOST THE ABILITY TO COMMUNICATE ON EITHER VHF RADIO OR COMMUNICATE WITH EACH OTHER ON THE INTERPHONE. THE ACFT HAD BEEN IN HVY RAIN BEFORE DEP.

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WE WERE TO ATTEND AN AIR SHOW. OUR DEP HAD BEEN DELAYED UNTIL LATE AFTERNOON AS WE WAITED FOR A LINE OF HVY SHOWERS/TSTMS TO PASS CLR OF OUR RTE. WE WOULD DEPART IFR; BUT ONLY THE FIRST 30-45 MINS OF THE FLT WOULD BE IN IFR CONDITIONS; WITH OUR DEST RPTING AND FORECASTING GOOD VFR. THE ACFT IS EQUIPPED WITH MODERN NAV/COM RADIOS AND AN ADF AND IS IFR CERTIFIED/CURRENT; NOTHING FANCY; BUT GOOD SOLID AVIONICS. WHILE WAITING FOR OPERATING TEMPS; I DIALED UP THE LCL ASOS ON THE #1 COM AND LISTENED TO IT. MY COPLT (REQUIRED CREW) THEN REQUESTED AND RECEIVED OUR CLRNC VIA THE OTHER COM RADIO. AFTER RUN-UP; OUR DEP INTENTIONS WERE ANNOUNCED ON THE LCL UNICOM FREQ AND WE DEPARTED IFR. THE FIRST SIGN OF TROUBLE CAME WHEN MY COPLT WAS UNABLE TO REACH THE DEP CTL FACILITY; IMMEDIATELY AFTER TKOF. I CONTINUED MY JOB AND FLEW THE AIRPLANE AS PER OUR CLRNC WHILE THE SIC DIALED IN THE 'NO RADIO' XPONDER CODE; AND UNSUCCESSFULLY TRIED ALTERNATE FREQ/RADIO COMBINATIONS. THE LOSS OF GND COM WAS CONCERNING; BUT WHAT REALLY MADE A DIFFERENCE WAS THAT THE INTERCOM HAD ALSO QUIT. VERBAL COM IN THIS PARTICULAR ACFT IS NEXT TO IMPOSSIBLE WITHOUT THE INTERCOM DUE TO THE ENG/PROP/WIND NOISE; NOT A SERIOUS PROB IN DAY VFR CONDITIONS; BUT WE WERE IFR AND IT WOULD SOON BE GETTING DARK. EVERYTHING IS MANUALLY OPERATED IN THIS ACFT AND THERE IS NO AUTOPLT; IT TRULY REQUIRES BOTH 'OPERATING LIMITATION' REQUIRED FLT CREW. WE WERE RELEGATED TO WRITING NOTES TO ONE ANOTHER AND MAKING HAND SIGNALS FOR EVEN THE SIMPLEST TASKS THAT REQUIRED CREW COORD. A 'LONG' 30 MINS INTO THE FLT; ONE OF THE 'COMBINATIONS' OF RADIO/HEADSET/SWITCHES WORKED AND WE WERE ABLE TO COMMUNICATE WITH NORFOLK APCH. ONLY 1 HEADSET AND 1 RADIO WORKED; BUT WITH GND COMS RESTORED; THE LACK OF VERBAL COM BTWN THE CREW WAS MUCH LESS OF A CONCERN; WE CONTINUED WRITING NOTES. SOON THEREAFTER; THE WX IMPROVED. WE DID HOWEVER CONTINUE IFR TO OUR DEST. BOTH MYSELF AND MY OTHER CREW MEMBER HAVE EXPERIENCED ALL SORTS OF EQUIP FAILURE IN THE PAST. BTWN US; WE HAVE DECADES AND TENS OF THOUSANDS OF HRS OF FLYING EXPERIENCE; BUT THIS PARTICULAR SERIES OF FAILURE EVENTS CAUSED US BOTH TO 'SIT UP AND PAY ATTN.' THE 'FINAL STRAW' THAT MADE THIS SUCH A MEMORABLE FLT WAS THE LOSS OF THE INTERCOM; NOT NORMALLY REGARDED AS A HIGH PRIORITY PIECE OF EQUIP; BUT COUPLED WITH COM FAILURE; CONDITIONS GOT SERIOUS IN A HURRY. IT WAS LATER DETERMINED THAT MOISTURE IN ONE OF THE PUSH-TO-TALK SWITCHES HAD MOST LIKELY CAUSED A STUCK/OPEN MIKE CONDITION. I GUESS WE OCCASIONALLY NEED TO BE 'TESTED' A BIT; JUST SO THAT WE DON'T BECOME TOO COMPLACENT. I'M JUST GLAD WE DIDN'T LOOSE THE NAV RADIOS.