bulid 12v switch off circuit
A simple solution could be a 230V relais. If the 230V get connected, it disconnects the TV of the 12 V power supply.







simulate this circuit &ndash; Schematic created using CircuitLab

If 230V is applied, the relais pulls and opens the switch. This disconnects the TV from the 12V power supply. If the 230AC leaves, the switch will jump back to its normal position and 12V is reconnected.