Flashers not working.

Was it raining ?
Does your windshield leak ?
Internationals seem to have a problem with water and fuse blocks.
Moisture turns those relays green inside.
Signal stat worn out ?

 

Ground. Always inspect and clean every grounding point you can find and even some you can't when mysterious and randomly intermittent electrical issues show up.

 

The flasher relay isn't really a relay, we just call it a flasher. They can act up if you have a bunch of LED lights because LEDs do not draw enough current to properly activate an old school flasher. If you have regular lights, the next spot after the flasher is the actual signal switch on your steering column. After that the power is split up to multiple circuits, so I can't see a single ground or a single power wire after the turn signal switch going bad and causing all the lights to not work. You could be losing flasher power into the turn signal switch. Power from the from flasher is wire 55A at the turn signal switch. This is big 12 gauge orange wire. The wire on the signal switch side is black. You might be losing power here, or the turn signal switch itself is going bad internally.