What was found
(CAN) DURING DESCENT SPEED APPROX. 240 KTS & ALT 8000 FT, RECEIVED LDG ADVISORY LIGHT FOR APPROX. 1 SECONDS ON MLG. BEHAVIOR OF A/C SIMILAR TO NORMAL LDG GEAR EXTENTION, I.E. FELT DRAG & "SOUND". AFTER SYS WENT BACK TO NORMAL. 1ST ACTION OF CREW SPEED REDUCTION. AFTER APPROX. 30-60 SEC SAME EVENT, WITH MAIN GEAR, OCCURED AGAIN. NORMAL GEAR EXT. PREFORMED & NORMAL INDICATION, FOLLOWED BY NORMAL LDG. MAINT INVEST. DETERMINED LT GEAR DOOR CLOSED SENSOR GAP TO BE FAR. LT GEAR DOOR CLOSED SENSOR ADJUSTED. A/C RT-SRV. THE CAUSE FOR UNCOMMANDED DOOR CYCLING AN INCORRECT RIGGING OF GEAR DOOR CLOSED SENSOR.