I can't say I've ever experienced this myself but I want to just so I can see it and have a play at fixing one myself.
It's one issue I've seen come and go a few times with various members over my years of membership on the forum.
Some members I've seen get issues the same way as the OP here and others seem to have induced it by trying to replace the stereo with built in hazard switch for a Single DIN aftermarket unit and their own Hazard Switch.
I have a good video that someone linked ages ago in another thread but don't have access to it at work as they have blocked me signing into Chrome with my personal Gmail account so can't get at my bookmarks
I'll try and re-post it later on tonight
It shows a great way of starting the truck bypassing the NATS to prove that it's the issue