[mix4fix]

Is that a relay or fuse issue?

[WGH]

Knowing the year and model of the car or bike might help. On my Subaru Outback it could be 100 different reasons, on my 1977 Wagoneer it would be the relay.

[mix4fix]

I can't explain it.

I pulled up to FedEx like I always do, and I turn on my flashers. The flashers would not work at all. They would work with the engine on, but not when the engine is off.

Later on, they started working normal again.

 

[AllanS]

I’d start with the relay.  As WGH mentioned year and model would help but something as easy as removing and reinstalling the relay could clean the contacts enough to restore function.  Since it’s working for now it’s hard to say what the problem is.  Running vs not could have been voltage difference.  Either way it sounds marginal.  You can also see if there is another relay in the panel to swap out for test if it happens again.

[WGH]

Hopefully the problem fixed itself and was a temporary glitch, like a piece of dust or bug got pinched between the contacts. The flasher was a $5 fix in my Jeep so the obviously first thing to try.

If all your vehicle's electronics are controlled by a computer like my Subaru Outback then restarting the car might have fixed the problem like restarting a Windows computer fixes a networking problem. Disconnecting the battery for 15 minutes is also a common suggestion to fix electronic gremlins.

I would think the flasher circuit is hard wired to the battery and should work whether the vehicle is on or off. Intermittent operation would indicate a short or the ground has corrosion and compromised. If the vehicle is started using a key then the ignition switch would be suspect. A heavy set of keys hanging from the switch will wear it out. The battery may be weak and getting ready to die, when the vehicle is running the flasher circuit is getting the full 12 volts.

For now do nothing. The first rule of mechanics is "If it works, don't f**k with it."

If the flasher becomes an intermittent problem, the only way to fix it is to wait until it doesn't work at all. I had intermittent problems with my Wagoneer all the time, my mechanic said "Drive it until it drops."

A technical service manual will have the wiring diagram for the flasher circuit. All solutions will lead to removing the dash.

[Rusty Jefferson]

Have your battery tested. Not just voltage, but available current. Cars can do funny things when a battery is weak but still just barely working. This ridiculously hot weather can add more stress.