Started the 1978 300 CD this morning, and a couple of seconds later, all of the electrical went dead. Motor was still running, but no lights, radio, nothing. Turned it off, and tried to restart, but it was as if the battery had been removed. This is the same vehicle that I have posted about recently where the high beams blew, and the heater blower fuse kept melting. We have tried to clean as many contacts as possible, but obviously there is some other gremlin we have missed. HELP!

 

sounds like a very easy repair,check the harness from the fuse box...

 

What was the final verdict on the lights and heater blower motor?

This sounds like perhaps a loose battery connection.

 

May have been a loose battery cable. The blower motor was probably bad, too. I think this is a classic example of multiple issues surfacing at once.

 

I side with the a loss of Ground or Positive Cable idea.

While this story is not quite the same I had driven my car 2 time and both times had normal starting, running and Charging.
I pulled in to get something to Eat and later when I got into my Car and turned the key; nothing happen at all.

To shorten the story it was the Battery that inside had evidently suffered some sort of internal short or open circit.

To that end I would recommend pulling the Battery and having it charged and load tested.