Identifying LINE and LOAD wires on the pictured TH115 power base

Use the printed rear wiring diagram when replacing a TH115 thermostat.

On the TH115 base shown in the attached photograph, the wires run from top to bottom as follows:

1. Black: LOAD to the heating system.
2. Black: L1 (L), incoming supply.
3. Red: L2 (N), incoming supply.
4. Red: LOAD to the heating system.

This order applies to the photographed base. Always follow the markings on the actual replacement unit. Two wires of the same color do not have the same function, and another generation may have a different arrangement.

Turn off the circuit at the electrical panel before accessing the wiring. A qualified electrician must distinguish the incoming supply from the heating load and use the correct 120 V or 240 V wiring diagram.

Sources: attached rear-base photograph and TH115-AF-GA owner’s guide (installation and wiring diagrams).