Electrical question... what's this?

[car barn]

What's this (other than a greasy mess)? Curious the about the box thing, and is that some kind of kill switch? Inside engine compartment, passenger side.

[CraigInPA]

VW "Diagnostic Socket". It's original equipment.

[car barn]

Thanks... so what's that black plastic thing at the bottom of the picture, next to the in-line fuse, used for?

[mondshine]

That little doughnut goes on the #1 spark plug lead for the "computer" diagnostic system.

Link

[BNMike]

And, look at the size of that Computer/Printer I used to have a calculator that displayed the numbers with those tubes.

BNMike

[Wildthings]

You don't need to do anything with the plug and wires, except leave them alone and not worry about them, they are fine just the way they are.