Alright, then it's either the fuel sender is bad, or the brake light failure device is bad, or possibly a wire is broke on the brake light system.
To check, disconnect the green/white wire at the fuel tank.
If the light stops flashing then the sender is bad or shorted.
If the light keeps flashing, then disconnect the brake light failure unit. It will look like a relay with three wires: Blue, black/yellow, green/white. The light should now stop flashing.
Reconnect it, the light will once again flash. Make sure the black/yellow wire to it is grounded.
Somehow ground the blue wire using a jumper of some sort. If the light stops flashing, there is a break in the blue wire running to the bulb, or the bulb is not grounded well.
If the light keeps flashing, and the brake light filament is for sure good, probably the brake light failure unit is bad.
