It could be that the Black-out Stroll is different from the video referenced earlier. I found one reference in an old book that said you change partners when the lights go out. It didn't have any other information. The song is by Joe Loss band (1939) with words and music by Tommie Connor.

The sheet music is offered for sale at several places.
This one says it has a diagram of the dance steps.
http://www.awm.gov.au/firstopac/bin/cgi-jsp.exe/shelf1.jsp?recno=50119&userId=&catTable=
This one says there are instructions.
http://www.sheetmusicwarehouse.co.uk/details.php?ref=9060

I found one place that has an audio clip of the music, but I couldn't get it to play on my computer. If it plays, see if it matches the dance in the previous video.
http://www.1940.co.uk/history/sound/sound.htm