I tried to fit LED lights to my trailer however had a problem with the indicator flashing faintly all the time.

I checked and there is current even when the indicators are not operating. I have a dim recollection that this issue has been raised before but I can't find anything on the forum.

Is this nornal or is there a fault? If normal is there a fix for it or do I throw away the LED's?

The LEDs draw less current then the filament bulbs causing the bulb out circuit to get confused. You have to add a extra load to the wire in parallel to the LED.
Where have you added LEDs? FL2, TD4 HSE
The flaming Orange!