A vehicle includes a power plant, an electrical port, and a controller. The controller is configured to transmit a signal to the inverter via a conductor of the port indicating a maximum power available. The signal may be transmitted responsive to indication of an off-board inverter being plugged into the port. The controller may be further configured to complete a circuit between the power plant and the inverter. The circuit may be completed responsive to an expected predefined reduction in peak voltage of the signal caused by the inverter.