Hello Angelini Max,
Thank you for your question. The command you are searching for is scsetledswitch #.
Value # can be 0 – OFF; 1 – ON.
All the commands for TST100 are here: https://wiki.teltonika-mobility.com/view/TST100_SMS/GPRS_Commands#Commands_Related_to_Features
Salve ho provato a dare il comando scsetledswitch 1 ma il faro non si accende
Have you received the response from the device to your cell phone after scsetledswitch 1 command was sent?