Whilst at Billing I got some Durite LED indicators and 'stop&tail' lights. Long story, but I've been thinking of getting some for a while as you'd be surprised at just how many clueless prats seem to want to slipstream 4 tonne of 101 ambi - especially at night...
Anyway, as the indicator LEDs have no real power they confuse the indicator relay into thinking the bulb is blown - therefore a load resistor is needed - or wire the LEDs in with another bulb (same effect). Without load, the indicator relay simply blinks ten to the dozen to inform you that a bulb is possibly blown.
A work-around is to use a phase generator - which is like an 'electronic flasher relay' - however these are not 'street legal' in the UK as they give no indication ('scuse pun) if you have a blown bulb.
I thought it interesting that in the high-tech chip controlled world we live in - it is still necessary to have a 50 year old design relay in order to pass the MOT and be street legal! :-)
Regards
Martyn