How can I make my TT lights flash unhooked from my truck?

You need a battery on the trailer to haul it anywhere. How will your emergency breakaway system work without a battery? Connect the battery to the typical trailer connectors. The trailer's umbilical should have a post that is connected to the battery (this is for charging with the vehicle while driving). Connect a heavy duty flasher in the umbilical slots for that 12V power and the marker/tail lights.