Product details:

Taco Sr503 3-Zone Switching Relay, 120 Vac, 24 Volt, 1800 Watt, Screw Holes Mounting "The Taco Sr503-4 Switching Relay Is The Best Choice For All Your Zoning Needs, With Advanced Powerport Cards, External Diagnostic Lights, Switchable Priority And Contractor Friendly Pc Board Layouts. Combined With The Time Proven Reliability Of The 00 Family Of Circulators And Thermostats, Total System Integrating Is Achieved. External Indicator Lights Provide Instant Diagnostic Feedback, Making A Snap Of Service Calls Or New Installation Start-Ups."