Step 1
Turn off the electrical supply to the Trane furnace at the main panel. Switch the designated circuit breaker to the "Off" position.
Step 2
Remove the thermostat cover from its wall mount to access the wiring terminals. Pull the cover straight off from the wall bracket.
Step 3
Locate the terminal marked “24 C.” This is the terminal connection for the 24-volt common wire.
Step 4
Strip half inch of insulation from the blue wire of the thermostat harness, using wire strippers.
Step 5
Connect the blue wire to the "24 C" terminal. Tighten the terminal screw clockwise, using a flat-head screwdriver. Reinstall the thermostat cover if all other work is complete.
Step 6
Remove the electrical access panel from the lower rear of the Trane furnace. Lift the panel up slightly, then pull it out from the bottom.
Step 7
Locate the thermostat control terminal bus. The bus is mounted vertically with four terminals marked "G," "W," "R" and "C." "C" is the designated terminal for the common wire.
Step 8
Strip half inch of insulation from the blue wire from the thermostat, using wire strippers.
Step 9
Connect the blue wire to the "C" terminal. Tighten the terminal screw with the screwdriver. Replace the furnace cover when work is completed.