Since the car has been sitting you should expect to have to clean most wire connections and terminals.
"Lucas" does not matter, a thin layer of corrosion leading to poor connection does.
Grounds in particular will cause all sort of problems.
Switches may sometimes be revived by simply exercising them, so long as the terminals are in good clean condition.
Fiberglass and rubber are non-conductive, so care must be taken to ensure good ground paths.
I have never had an issue due to adding ground points to any car.