GIV FLT CREW LOSES ALL PFD AND NAV DISPLAY INFO DURING MISSED APCH IN IMC CONDITIONS. RESTORE PARTIAL OPERATION AND LAND SAFELY ON ILS APCH.

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MMU HAS NO ASOS; TEB AND EWR WERE LNDG RWY 6 AND RWY 4. ATC VECTORED US FOR RNAV 5 APCH. WX WAS FROM CDW ASOS OR EWR. WE HAD NO WX FOR MMU. DURING GPS MISSED APCH TO RWY 5 AT MINIMUMS (860 FT) WE SELECTED GAR MODE (GULFSTREAM IV). WE LOST ALL NAV DISPLAY DATA ON BOTH PFD'S AND NAV DISPLAYS; BOTH FMS'S LOST ALL DATA AND FMS KEY PAD LOCKED (UNABLE ANY INPUTS). BOTH FLT GUIDANCE COMPUTERS FAILED; FGCP; AUTOPLT; ELECTRIC TRIM; YAW DAMPER; AND AUTOTHROTTLES HAD FAILED. FGCP HDG WENT TO 000 DEG HDG; ALT SELECTOR WENT TO 100 FT. V-BARS INITIALLY COMMANDED A DSCNT (THE 100 FT) IN THE SELECTOR WINDOW. MISSED APCH ALT WAS 2300 FT AS PER FDC NOTAM. MY ALT DID VARY SOME +/-200 FT HANDLING AN ACFT WITH NOW ONLY MANUAL TRIM DURING PWR AND CONFIGN CHANGES. ACFT HAD BEEN CONFIGURED FULL FLAPS FOR LNDG AND NOW FULL PWR FOR GAR AND FLAPS UP TO 20 DEGS WITH NO ELECTRIC TRIM DURING THE GAR (HANDS FULL). AS THIS IS A STANDALONE APCH; CHARTS DO NOT SHOW FREQ OF ANY LAND-BASED NAVAIDS (BIG MISTAKE). WE WERE TO FLY DIRECT TO MOREE; AN NDB AND HOLD. THE COPLT ENTERED THE FREQ AND WE PROCEEDED IN THE DIRECTION OF THE FIX. ATC WAS ADVISED OF OUR MISSED APCH AND THAT WE HAD LOST EQUIP REQUESTING A VECTOR SO WE COULD SORT OUT OUR FAILURES AND A PLAN OF ACTION. ONCE LEVEL; WE RESET OUR FGC CIRCUIT BREAKERS AND RECOVERING AUTOPLT; TRIM; AND YAW DAMPER; NO AUTOTHROTTLE FMS OR FGCP. WE REQUESTED VECTORS TO EWR; DUE TO A LEVEL 5 TSTM THEY WERE CLOSING OPS. WE WERE VECTORED BACK TO MMU FOR THE ILS 23 APCH WHILE WORKING OUR WAY AROUND LEVEL 4 AND 5 CELLS. THE ILS 23 APCH WOULD HAVE BEEN OUR FIRST CHOICE HAD WE HAD MMU WIND/WX. MMU NEEDS AN ASOS; ALSO RNAV APCHS NEED FREQS LISTED AS BACKUP. BOTH GULFSTREAM AND HONEYWELL SPENT SEVERAL DAYS CHKING OUT EQUIP AND CHANGING OUT UNITS. I DELAYED IN THIS RPT HOPING FOR SOME ANSWERS. NONE YET!