What was found
(CAN) THE NR 1 ENGINE OIL PRESSURE WARNING LIGHT CAME ON DURING ROTATION AND CONTINUED TO FLICKER DURING THE INITIAL CLIMB. THE OIL PRESSURE ON THE GAUGE WAS STEADY AND NORMAL. ONCE THE ACFT HAD CLIMBED TO A SAFE ALTITUDE THE ENGINE WAS SHUTDOWN IAW THE QRH AND THE ACFT RETURNED TO THE DEPARTURE AIRPORT. MX T/S FOUND A CHAFED WIRE (1D20-2) ADJACENT TO AND FOR THE NR 1 ENGINE OIL PRESSURE SWITCH. THE WIRE WAS REPAIRED IAW STANDARD PRACTICES. THE NR 1 ENGINE OIL PRESSURE SWITCH WAS ALSO REPLACED. (SWITCH P/N 8D1437, S/N 1581).