The Zetron Model 18/18+ is a wireless telemetry module used in Control Link systems to replace leased telephone lines for discrete on/off or analog monitoring and control of industrial equipment. Common failure points for this class include power supply degradation, RF interference causing loss of link, firmware corruption leading to unresponsive status displays, and connector corrosion affecting data and power contacts. First‑check diagnostics: verify 12 V DC input voltage and current draw against spec; inspect all RJ45/connector pins for continuity and signs of oxidation; review the module’s diagnostic LEDs or serial log for error codes indicating link loss or firmware errors.[oss-gpt-20b]