I have PLC type TSX 3721101 and it has the lamp I/O IS red , while RUN lamp is green & TER lamp is orange, What is the problem?
It seems from the error that PLC is in RUN mode and its communicating. There seems to be an issue with IO's etc.
IO LED (red) is lit to show a fault relating to the inputs/outputs: supply fault or at least one channel tripped, module missing, not configured or out of service. So kindly go online with PL7 software and troubleshoot and check for any errors on modules.
Suggestion is to trouleshoot, identify the faulty modules or else if any and repalce or correct the same. The I/O error must go.