What was found
NR 1 GPS MESSAGE "HEADING REQUIRED" RENDERING, GPS AND NR 1 AUTOPILOT INOPERATIVE. VECTORED SO ACFT STAYED ON HEADING MODE. AUTOPILOT NR 2 SELECTED BUT DID NOT ENGAGE. NOT SUCCESSFUL AFTER SEVERAL ATTEMPTS. RETURN TO AIRPORT. LANDED NORMAL. MX CHECKED WIRING FROM NR 2 NPU TO SWITCH BOX 81VU21, FOUND NORMAL. RESET NR 2 NPU, ACCOMPLISHED CHECK OF F/O HSI, OP'S CHECKED GOOD IAW 34-53-01. NR 2 GPS SENSOR READ OUT FOUND NORMAL IAW 34-53-01. ACFT RETURNED TO SERVICE.