What was found
AFTER LIFT OFF, APPROX 200 AGL, ELEV PRESS CAUTION LIGHT ILLUMINATED. ALL 3 HYD SYSTEMS READ 3000 PSI. NR 3 HYD ISO VALVE WAS OUT AND DARK. CAUTION LIGHT STAYED ILLUMINATED THROUGHOUT FLIGHT. CAUTION LIGHT WENT OUT AND NR 3 HYD DROPPED AFTER LANDING. RETURNED TO FIELD. LANDING UNEVENTFUL. AS PRECAUTIONARY MEASURE, REPLACED NR 3 HYD PRESSURE SWITCH-C IAW AMM 29-30-11-000-801, 29-30-11-400-801. PERFORMED FUNCTIONAL TEST OF NR 3 HYD SYS IAW AMM 29-12-00-720-801. FUNCTIONAL TEST FAILED. ELEVATOR PRESSURE CAUTION ILLUMINATED. ALSO, NR 2 HYD ISO VALVE CAUTION DID NOT ILLUMINATE DURING FUNCTIONAL TEST. INSPECTED NR 2 HYD ISO VALVE AND FOUND BOTH PRESSURE SWITCH CONNECTORS DISCONNECTED. CONNECTED BOTH PRESSURE SWITCH CONNECTORS IAW AMM 29-30-11-400-801. PERFORMED FUNCTIONAL TEST OF NR 3 HYD SYS IAW AMM 29-12-00-720-801. FUNCTIONAL TEST GOOD. ELEVATOR PRESSURE CAUTION DID NOT ILLUMINATE AND NR 2 HYD ISO VALVE CAUTION EXTINGUISHED/ILLUMINATED NORMALLY. RETURNED TO SERVICE.