Probably corrosion on terminals inside the hazard switch. If you remove and unplug it, you will see how to gently pry on the side catches and take it apart. Careful, springs and steel balls inside. Clean the contact surfaces with a rubber eraser and use contact grease. All the turn sig wiring goes thru the switch. Known failure point.

Justice, use a "heavy duty" flasher when trailering to get the light flash interval right. The heavier load of thee trailer lights makes the stock flasher work too fast...

Not responsible for advice not taken...