Taco Zone Valve Controls work with 2-, 3-, or 4-wire zone valves. All are fuse protected, it also includes 2 isolated end switches and a built-in priority switch. The contractor friendly PC board layout eliminates incorrect wiring and the in.unfinished in. look of conventional zone valve installations. The sturdy screw connections add even more reliability, while the external indicator lights provide instant diagnostic feedback to reduce installation time and troubleshooting. For those larger jobs, the -EXP controls can be expanded up to 120 zones with priority. All Taco Zone Valve Controls are UL Listed and are available in 3, 4, 5 and 6 zones. External Diagnostics: The indicator lights show full functionality of the products wired to the zone valve control. The green light indicates power is connected. When the thermostat calls for heat, both the appropriate zone valve and yellow indicating light are energized.