The POWER RELAY is shown at LOWER RIGHT OF BOX.
It is connected to the two right terminals labeled "Booster Pump."

How To Wire Power To The PCS2

Connect the 115vac "hot side" for the PCS2 to the rightmost terminal.
This is the RELAY INPUT terminal.

Connect the PCS2 outlet "hot side" to the second terminal from the right.
This is the RELAY OUTPUT terminal.

Wire the PCS2 ground and neutral directly to the PCS2 outlet box.

In simple terms, the relay controls the hot side of the PCS2 power.

The RELAY closes during SOLAR ON to power the PCS2.

Wiring DiagramUsing An External Relay To Expand Control Capabilities

First Generation SolarAttic Solar Pool Heater