The resistor is wired in parallel as it is there to apply the extra load that the relay needs to see to flash correctly, not drop the voltage to the led's.
The other option is to buy a dual load indicator relay. These have a fixed flash rate and will work with either led's, bulbs, or a mixture.
Something like the below. This should be suitable for use in the standard Sierra wiring setup.
http://www.ebay.co.uk/itm/LED-FLASHE...em5d2f4 c7b2f