What was found
AFTER TAKEOFF, AND AFTER GEAR RETRACTION. THE NOSE LANDING GEAR RED UNSAFE LIGHT ILLUMINATED, FOLLOWED BY A RUBBER BURNING ODOR. RED LIGHT WOULD STAY ON A FEW MINUTES AND GO OFF, THEN COME BACK ON UNTIL LANDING. THE FLIGHT DECLARED AN EMERGENCY AND RETURNED TO DEPARTURE WITHOUT FURTHER INCIDENT. LANDED WITH 3 GREEN AND UNDER MAX LANDING WEIGHT. AFTER NORMAL LANDING, MAINTENANCE INSTALLED ALL THREE GEAR PINS FROM AIRCRAFT. MAINTENANCE REPLACED D1-32 NOSE GEAR LOCKED SENSOR IAW AMM 32-60-05, AND NOSE GEAR LOCKED, WIRING HARNESS IAW SWPM 20-61-00. ALSO, DUE TO ODOR IN THE CABIN AFTER TAKE OFF, REMOVED AND REPLACED THE LT PRESSURE REGULATOR VALVE IAW AMM 21-31-01. AIRCRAFT WAS GROUNDED.