Have you tried the wires around the other way ? LED's are biased and need to be wired the correct way round unlike filament bulbs which don't matter.
On my TR250 I fitted an adjustable flasher relay ( ebay item about £5 ). This allowed filament bulbs and LED's on the same circuit to function, the adjustable knob on the relay setting the flashing speed. No need to fit extra resistors either.
Last edited by Lucky@LeMans; 31st March 2020 at 20:47..