One other thing I've Run into may be helpful here. Many flashers are extremely resistence sensative. We don't know if front signals were connected when rears were blinking fast. Rear flashers with no fronts splits resistence in half causing the quick flash. Also using dissimilar bulbs(halogen, led) can create further quandry. First things first,check wiring. Also, don't wind two power wires together to use both filiments for brighter light, too much resistence.
Good luck
