Just sharing this story should anyone else ever encounter this issue.

My 2019 FLHTCUTG - I was coming home from a ride to Upstate NY and pulled into a Service Station to fill up before I hit the last leg of the journey home. Got in front of the pumps and flipped the ignition switch to accessory which I do sometimes so I can listen to my tunes.

Did not pay attention to the dash board, but heard the security chirp. As I was putting the credit card into the pump I noticed the 4-way flashers were on. Hmmm....must have bumped the 4-way flasher switch when getting off the bike I thought.

Reached over and hit the switch, but the 4-ways kept flashing. Hit it a couple more times - same thing not shutting off. WTF???

Filled the tank with the 4-ways flashing and feeling like an idiot. Put the nozzle back in the pump, got my receipt and proceeded to analyze what was occurring.

Was the bike trying to tell me something with the 4-way flashers? Was something malfunctioning and this was a code of some sort? Never read anything about this in the service manual etc.

Proceeded to turn the ignition switch all the way off and then allow it to reboot to start-up, no joy kept flashing. Did it a couple more times putting it to accessory and hitting the 4-way flasher switch - still no joy kept flashing; interesting. Do not want to ride the last 60 miles home on the highway with the 4-ways flashing if I don't have to.

So I turned the ignition switch off, removed the side panel cover, put the switch to on with the FOB nearby and allowed the security to chirp, then pulled the main fuse. NOTE if you do not let the security chirp and you have a siren it will make a lot of noise because of the back-up battery, don't ask me how I know.

Turned the switch to off while the main fuse was out and let it set for a couple of minutes. Put the fuse back in and no more flashing - good; bike started up normal. Got home and tried to replicate the issue, everything working as normal, 4-ways would turn on and off, security system worked normally, chirped and flashed the signals 4-way - strange indeed.

ANOTHER NOTE: I do have LED bulbs installed in all the blinker lights; however, they have been in there over a year and have not caused any issues.

Going to see if there are any codes and will update according later, for now just going to relax as it was an unexpected 95 degrees for the last 2 hours of my trip.

EDIT: Pulled the codes and the only one there was a BCM: B2285h (Rear Brake Configuration Historical).

 

Mine does something like that right before the key fob battery goes dead.

 

I had something similar about four years ago on my '14; I had the flashers on and turned the ignition switch from ACC to off. They wouldn't shut off. But they did when I put the ignition back in ACC. I tried it again, same thing. Haven't done it since.

I thought maybe it might be some undocumented 'feature'. Like maybe keep someone from turning them off if you've left for a bit.

 

Remember, you have to have your switch in the on position to turn the 4way's on or off.
Haven't tried Acc position. But you can't turn on or off in the OFF position.

 

Correct, they will turn on & off in the Accessory position. Did not matter in this case even when turning ignition off they continued to flash.

 

Correct, the 4way flashers stay on until canceled out with the turn signal switches. Switch on & both held in at the same time for about 5 seconds. The switch can be on or off, it doesn't matter once the 4 ways are activated.

 

The OP has a 2019. The 4ways are no longer activated/deactivated with the turn signal switches. The Hazard warning (4way) switch is on the right hand controls.

 

I overlooked that !! My Bad !

 

I call this computer bugs of the newer bikes “CAN BLUES”

fortunately they are mostly harmless.

 

I have a 2021 Tri Glide Ultra with less than 2k miles.
I was headed home on a Farm to Market road when I came upon a flag man stopping traffic in a construction zone. It was 95* with no shade in site, and that M8 makes plenty of heat, so I turned the switch to ACC. I looked in my mirror to see traffic coming up behind me so I switched on the four way flashers.
After a bit it was time to go, flipped the switch back to IGN, hit the start button, and… nothing!
I tried every combination of Clutch-Neutral-Brake-Switches etc… nothing!
When cycling the switch, the dash reacted as normal, all lights and gauges did what they always do. I did like you, pulled the fuse, reset the switch, everything… nothing!
In total desperation I got out the Owners Manual and looked for info on the neutral safety switch. I found the instructions for a Tipped Bike, even though my odometer was not reading “TIP, I followed the steps to reset it and, voila! It started.
I’ve tried a couple of times to replicate it and have been unsuccessful, I’m hoping it was just a fluke. But after reading your post, it sure seems to be close to the same thing.