The Thermostat Cable connects the Thermostat to the Control Box. 

The HEAT/COOL only application requires only Six Conductors. 

The COOL/FURNACE/HEAT STRIP,and the COOL/FURNACE/HEAT PUMP models require Seven Conductors. 

It is common for most manufacturers to install an eight-conductor thermostat cable. 

The cable is easily checked by an ohmmeter. 

Disconnect the thermostat cable from the control box and the thermostat. 

Each wire should have continuity from end to end 

No continuity should exist between any of the wires. 

Continuity between wires indicates a problem (e.g., a staple) in the cable. 

If you don’t have continuity end to end on one or more wires you may try using an unused conductor if available. 

In some situations there may be a loose connection at a hidden wire harness.