Good evening. If you are using Lucas LD109 sidelights the earthing method is rather crude being a brass 'tongue' which earths the reflector/bulb holder onto the mounting bolt. This is fraught with potential (no pun intended) problems.
I use a twin core cable and solder the earth wire to the bulb holder. Lucas modified the earthing arrangement later by attaching a female bullet connector to the bulb holder and employed a bullet connector on the earth wire.
Regards
Stuart

Location: Staffordshire, the creative county

Thanks - I will have a look at the earthing arrangements and see if I can improve matters.
Regards
Colin

Some useful tips here.