Check to see if you have power wired to both the pwr1 and pwr2 terminals. If not, wire your single power source to both pwr1 and pw42 (ie; jump pwr1 over to pwr2). The EIS-40xFX units have redundant power ports. If either of the power ports does not have power applied then the yellow Fault LED turns on. Note, the Fault LED will also turn on if there is a failure onthe RJ45 or Fiber Optic ports. Also if you lose pwr1 or pwr2, the local relay will alarm (de-energize and close) if you lose power to pwr1 or pwr2.