Finding the power wires to the rear lights and splicing wires is too complex... better to hookup a 3D accelerometer and light sensitive diode array to a microprocessor (LOM processor) to detect when you are braking, turning and driving in the dark... then to avoid doing any complex wiring, you need bluetooth activated lights on the trailer... all activated from the one simple LOM processor. You might be able to purchased the whole setup from Jina for 50c.