Head light has been playing up so I pulled the light off to find the socket that plugs into rear of head light is crusty, looks light it overheated and the plastic around the metal spade connectors is melted, looking for some advice or direction before I start pulling things off.

Cheers

If the terminal has been loose, or a "dry joint" it would have arced causing overheating, So yes, it would cause the plastic to melt and go crusty.

Clean the terminals with emery cloth back to bare metal, make sure they are a tight fit, and re-connect after coating them with a dielectric grease (usually available from any of the auto stores, Permatex or Molykote etc,etc.)

 Black should be the earth,  current flow with both high and low beam.

Dry joints/loose connections can come and go for some time, the arcing can establish continuity sometimes, but eventually ends up in total failure.

(the hottest part of the circuit should be the filement in the globe (highest resistance), but seeing as the connection was dicky the highest resitance moved house from the filement to the connector, hence, the heat.)