I have a 1971 164.

OK it's not really graphic as much as it is disturbing. This weekend I decided to dive in and sort out my intermittent headlight issues. Sometimes one will go out on low beam but be fine on high, etc. I wiggled the wires around under the bonnet and both came on. Figured OK there's a loose wire somewhere.

I stripped back some of the electrical tape (shudder) around the relay and found this:



Stripped back more of the electrical tape and what looks like factory rubber wire sheath and found more:



All the way back to the steering column switch in fact:



Even the dashboard on/off switch seemed toasted around the white wire:



There was electrical tape concealing all of this, so it wasn't me who did it :) I bought this car more than four years ago and have been driving it this way ever since! Well that is terrifying.

I am going to replace the wires obviously but what could have caused this and how can I prevent it in the future? Too much current on what looks to be the high beam wire?

Here's a diagram of the relay: