Spitfire heater blower doesn't turn off

[Charley Maresca <maresca@abc.org>]

Hi.  I'm working on a 1970 Spitfire.  When I repaired the non-blinking turn
signals (loose connection at the fuse box) the heater blower turned on. 
It does not turn off.  When I removed the switch, I discovered the cable
was conducting electricity to the switch body.  I took the heater box
completely out of the car this weekend, and could discover no obvious
or not-so-obvious short circuit.   So now am I looking for an otherwise
undiscoverable short, or is there some other answer?  Thanks for any
help.