How rapid is the blink? Does it blink like a strobe light, once every half second, every few seconds etc?
Possibly a low battery or an auto reset circuit breaker. Maybe a loose wire on the battery terminals.
Do you have a voltage meter? It would probably be very helpful to know what the battery is doing while the blinking is occurring. Does the voltage drop at the battery with each blink or does it hold steady? Does the voltage fluctuate with the blinking a the fuse panel?