You've probably got a flashing fuse placed into the interior light fuse position, there are two fuse boxes, one below the steering area, and one under the hood. Find the interior lights fuse and replace it.
There is a faulty fuse that goes to the interior lights. There could also be a short in the wiring that leads to the lights.
check the battery and or alternator
The flashing lights are probably the factory alarm.
the fuse is blown.
Probably a loose connection in the wiring or the bulb socket.
the flashing lights are the fireflies or the beetles :)
Is door ajar light on also?
locate the fuse to the interior lights and remove it. On our 98 Explorer you turn the dash light adjustment switch off, next to the headlight switch.
Possible headlight switch. Try wiggling the controls to see if it stop or gets worse.
pretty easy really, make sure your interior lights are not turned on. Your headlights control should also be the interior light controller. Turn it clockwise or counterclockwise to turn your interior lights off. You'll run your battery down if you dont
People with epilepsy can have their seizures triggered by flashing lights
The flashing lights on aircraft are anti-collision lights, so they can be seen more easily.