There could be many reasons the trailer lights can go awry but most of the time it can be fixed by anyone who has little skills.Today, we have LEDs in place of the globes and much more complicated devices, yet the trailer lights i.e. the running/brake lights and indicators are in the same arrangement; wiring running through the light fittings and a plug connecting to the tow vehicle. Tools required Check the plug and socket Check the globe Light Fittings Check Voltage In case it is not, you might have to seek professional help.