CESSNA 414 PLTS ON MAINT FLT TEST AFTER AN ANNUAL INSPECTION LOST VOR AND COMPASS HEADING EQUIP AND BECAME LOST RESULTING IN PENETRATION OF A PROHIBITED AIRSPACE. APCH CTLR PROVIDED ASSISTANCE TO SUCCESSFUL LNDG.

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INADVERTENTLY PENETRATED PROHIBITED AREA P49 ON A MAINT FLT TEST AFTER MULTIPLE NAV SYS/ACFT SYS FAILURES. PF WAS PVT MULTI-SEL WITH NO INST RATING AND WAS UNFAMILIAR WITH AREA. I WAS WORKING RADIOS AND TROUBLESHOOTING SYS FAILURES. WE HAD RADAR SVC. ATC ADVISED OF AIRSPACE PENETRATION. WE ESSENTIALLY HAD NO MEANS TO NAV OTHER THAN GND REF (LANDMARKS). WE WERE ONLY ABLE TO FIND PWG (BASE) AFTER FINDING AND IDENTING HWY 84. WET COMPASS WAS INOP DUE TO 'HIGH' WINDSCREEN DE-ICE 'STUCK' IN 'ON' POS AFTER OP TEST; CAUSING WET COMPASS TO SWING AND READ IN ERROR. DIRECTIONAL GYROSCOPE INOP DUE TO HEADING BUG TURNING COMPASS CARDS WHEN USED; MAKING THEM READ IN ERROR. WE WERE ESSENTIALLY LOST. VOR NAV WAS IMPOSSIBLE DUE TO LED DIGITS BEING BURNED OUT; COULDN'T TUNE VOR. IN RETROSPECT; I SHOULD HAVE DECLARED AN EMER; AND CLBED ABOVE THE AIRSPACE. HOWEVER; WE HAD OUR HANDS FULL TO JUST TERMINATE THE FLT SAFELY. WE WERE VERY WORRIED ABOUT SMOKE/FIRE DUE TO THE FAULTY WINDSCREEN HEAT SWITCH. FIRST FLT OF ACFT AFTER EXTENSIVE ANNUAL INSPECTION. CALLED ATC UPON LNDG AND TRIED TO EXPLAIN SIT.