The message
from Tony Polson contains these words:

Thanks Andy. You're right, the red is definitely the earth. The red
wire is clearly earthed to the metal chassis of the projector.

If you're not doing a museum quality restoration I'd be tempted to
replace the mains lead completely with a modern standard one so some
other poor sod doesn't come unstuck at a later date.

--
Skipweasel
Pay no attention to that man behind the curtain.