Andy, it just about has to be a difference in current drain between the two sides. Most often when one side is faster than the other a bulb is out but presumably you've swarmed all over that. Can't make a case for a bad wire or short because should that be the case you would lose the operation of the circuit. Obvious question, are you using the same wattage bulbs on each side, flasher should react the same to the same current demand on either side, bet you've got an imbalance, check those bulbs. No two anything are exactly the same so you could make a case for a borderline difference and a very sensitive flasher but that's pretty far out! I go with the above. Les