A B757-200 IN CLB AT FL290 DECLARED AN EMER AND DIVERTED DUE TO STRONG ELECTRICAL BURNING ODOR IN COCKPIT AND FORWARD CABIN.

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AS WE WERE CLIMBING THRU FL290; I SMELLED A FUNNY ODOR THAT I INITIALLY COULD NOT IDENTIFY. I TOLD THE CAPT BUT HE DID NOT SMELL IT. AFTER A FEW SECONDS; THE SMELL GOT STRONGER AND WE BOTH PUT ON OUR OXY MASKS AS PER QRC. WE IDENTIFIED THE ODOR AS BEING ELECTRICAL IN NATURE (PROBABLY BURNED WIRING OR INSULATION). AT NO TIME WAS THERE SMOKE PRESENT. WE NOTIFIED ATC OF THE SIT AND INTENTIONS TO RETURN TO ZZZ. I RAN THE QRC AND THE FOLLOW-UP ACTIONS. WE TOLD ATC WE WANTED PRIORITY HANDLING FOR THE RETURN TO ZZZ; BUT AS WE DSNDED WE ELECTED TO GO TO ZZZ1 SINCE IT WAS THE NEAREST SUITABLE ARPT. WE NOTIFIED DISPATCH OF THE SIT AND TOLD THE FA TO DO A CABIN ADVISORY. ONE OF THE FA'S NOTIFIED US THAT THE ODOR/FUMES HAD ENTERED THE CABIN AND COULD BE SMELLED AS FAR BACK AS DOORS 2 L/R. WE ELECTED TO DO A VISUAL APCH TO RWY 25 INTO ZZZ1. AFTER LNDG; I REMOVED MY MASK AND NOTICED THAT THE FUMES/ODOR HAD DISSIPATED. THE FIRE CHIEF INFORMED US THAT THEY DID NOT SEE ANY SIGNS OF SMOKE OR FIRE AND WE ELECTED TO TAXI TO A LOCATION IN FRONT OF FBO. THE FA'S ALSO INFORMED US THAT THE FUMES HAD DISSIPATED IN THE CABIN AS WELL. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE RPTR STATED THE ELECTRICAL BURNING FUMES WERE FIRST DETECTED IN THE COCKPIT AND O2 MASKS WERE REQUIRED DUE TO THE STRONG ODOR AND FUMES. THE RPTR SAID AN EMER WAS DECLARED AND A DIVERSION WAS MADE TO THE NEAREST SUITABLE ARPT. THE RPTR STATED A CABIN ATTENDANT RPTED THE ODOR/FUMES COULD BE SMELLED IN THE FORWARD CABIN AS FAR BACK AS DOOR 2 L. THE RPTR SAID COMPANY MAINT LATER RPTED FINDING AN OVERHEATED WIRE BUNDLE BEHIND THE FO'S INST PANEL. THE RPTR STATED THERE WAS NO INDICATION OF COOLING FAN FAILURE OR LOW FLOW COOLING DETECTION AND ALL THE INSTRUMENTATION ON THE PANEL WAS OPERATING. THE RPTR SAID NO CIRCUIT BREAKERS WERE FOUND TRIPPED.