As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
SHORTLY AFTER TAKEOFF, RECEIVED "GEAR UP DISAGREE" WITH NOSE ICON AMBER, IT WENT OUT AND THEN REAPPEARED WITHIN A COUPLE OF MINUTES, THIS TIME RED. QRH AND LANDED WITH NORMAL INDICATIONS. INSTALLED NLG AND MLG DOWNLOCK PINS AND PLACED ON MEL REF 213702/2 FOR MEL. INTERROGATED PSEU. FOUND S21 SHORTED. R & R NR 1 NLG DOWNLOCK PROX SWITCH HARNESS. REF AMM32-61-05. OPS CHECK GOOD. REMOVED PLACARD, REMOVED MEL.