What was found
AIRCRAFT WAS GROUNDED: ON TAKEOFF #1 ENGINE OIL FILTER BYPASS LIGHT ILLUMINATED. ENGINE OIL PRESSURE CONSTANT 30 PSI. MAX OIL TEMP 105. NO VIBRATION. N1 & N2 NORMAL. EMERGENCY DECLARED, FLIGHT DIVERTED TO JFK, LANDING SAFELY. MAINTENANCE FOUND SCAVENGE OIL FILTER DIFFERENTIAL PRESSURE SWITCH STUCK IN THE BYPASS POSITION. REPLACED THE SCAVENGE OIL FILTER DIFFERENTIAL PRESSURE SWITCH (TRANSMITTER) PER AMM 79-21-07. ACCOMPLISHED SATISFACTORY ENGINE IDLE RUN AND LEAK CHECKS.