What was found
DURING DESCENT INTO ONT, WITH POWER REDUCED TO IDLE, NR 1 ENG LOW OIL PRESS LIGHT ILLUMINATED. OIL PRESS IND 42 PSI. SHUT NR 1 ENGINE DOWN, OIL PRESS WAS 7 PSI DURING DESCENT AND APPROACH FOR 8 MINUTES. INSPECTED MAIN OIL FILTER, NO CONTAMINATION FOUND. CHECKED CONNECTORS AND WIRING, CLEANED CONTACTS ON OIL PRESSURE WARNING SWITCH AND OIL PRESSURE WARNING SWITCH, NO DEFECTS NOTED. NON SUBSEQUENT FLIGHT DURING TAXI OUT, NR 1 LOW OIL PRESSURE LIGHT ILLUMINATED, OIL PRESS INDICATED 42 PSI AT IDLE. VERIFIED OIL PRESSURE SWITCH DEFECTIVE. REPLACED SWITCH.