BE90 CAPTAIN FAILS TO WRITE UP A 'MINOR' ELECTRICAL PROBLEM WITH A LIGHT RHEOSTAT. SHORTLY THEREAFTER THE ACFT DECLARES AN EMERGENCY AND DIVERTS DUE TO SMOKE IN THE COCKPIT TRACED TO THE SAME RHEOSTAT.

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I LEARNED THIS MORNING THAT AN ACFT WHICH I HAD FLOWN HAD EXPERIENCED SMOKE IN THE COCKPIT IMMEDIATELY AFTER A FLT WHICH I HAD TAKEN. A COUPLE DAYS EARLIER I HAD FLOWN THE SAME PLANE AND NOTICED THAT THE FUEL PANEL RHEOSTAT LIGHT WAS NOT DIMMING. IT EITHER WOULD WORK ON BRIGHT OR WOULD BE OFF. SO I HAD CONTINUED MY FLT ON THAT DAY WITH THE LIGHT OFF AND SWITCH TURNED OFF. I HAD NOT WRITTEN UP THE BROKEN RHEOSTAT LIGHT WHICH WAS MY MISTAKE. THE NEXT DAY OR FOLLOWING DAY; I HAD MENTIONED IT TO THE CHIEF OF MAINT THAT IT WAS NOT WORKING PROPERLY. HE SAID HE WOULD LOOK AT IT AND SHRUGGED IT OFF AS A MINOR DETAIL. HE LOOKED AT IT THE SAME WAY AS I HAD LOOKED AT IT. LAST NIGHT; WHICH IS THE DAY I MENTIONED IT TO THE MECH; ANOTHER FLT IMMEDIATELY GOES OUT AFTER I HAD FLOWN THAT PLANE MOSTLY WITH THE LIGHT TURNED OFF DUE TO IT BEING BRIGHTER INFLT THAN OTHER LIGHTS AND ALSO DUE TO IT BEING AN ANNOYANCE TO ME. THE FLT DIDN'T MAKE IT TO IT'S DEST BECAUSE THE PLT HAD SMOKE IN THE COCKPIT AND DECLARED AN EMER AND LANDED PRIOR TO DEST. THE REASON FOR THE SMOKE WAS DUE TO A SHORTED RHEOSTAT. IT IS UNBELIEVABLE SOMETHING SO MINOR COULD CAUSE THE MAJOR EMER. THIS IS A LEARNING EXPERIENCE FOR ME; AND I WILL NOT TREAT MINOR ELECTRICAL ITEMS AS MINOR PROBS. THE PROB SHOULD HAVE BEEN NOTED AS A DISCREPANCY; TOO; IN OUR DISCREPANCY FORM.