OK, back to basics:

Lucas changed from bullet connectors to spade type in the late 1950's or very early 1960's. Looking at them, you'd think it was a normal setup.

Wrong! Take a close look at the insides of the little original fuse box on the firewall. Still look normal? OK, think about it...only Lucas would have used rivets to make the connections between the wire terminals and the fuse clips. These connectors (in wet weather locations) are prone to getting corrosion between the metal surfaces.

You can't see it, but it's in there. The only solution - other than replacing the fuse boxes and whatever other Lucas-style fitments your car has - is to drill out the rivets, clean the corrosion and then solder the pieces back together.

This is one reason that Lucas is known as the 'Prince of Darkness': any electrical component can fail due to these miserable excuses for connections. You'd think that a major company like Lucas, based in one of the wettest countries in the world, would have designed something that would stand up to moisture better.

But, as the British are fond of explaining, "Gentlemen simply do not motor about after dark."

:-)