Lucas C35A Regulator

[Stuart Giles]

This is a photo of the rear of the switch. 
Someone has added an extra wire (blue) soldered near to the ignition light  from the D terminal. Disconnecting it causes the ignition light to stay on continuously. 
Is this a fix for broken switch internals?

Looks like a fix for the common problem of the switch panel's metal track to the ignition warning lamp having snapped. You can just see the break on this 'work in progress' switch panel I was restoring a few years ago. I just soldered a piece of copper wire across the break.