As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
ON TAKEOFF DURING ROTATION, THE LEFT IGNITION LIGHT ILLUMINATED AND STAYED ON UNTIL ABOUT 5,500 FEET. ALL ENGINE INSTRUMENTS APPEARED NORMAL. CREW RETURNED TO DTW. MAINTENANCE RAN AIRCRAFT FOR 30 MINUTES AND COULD NOT DUPLICATE ON GROUND. MAINTENANCE REPLACED P3 SWITCH IAW SF340 AMM 74-30-20. PERFORMED OPS CHECK, ALL CHECKS GOOD.