Battery cut-off switch

If you don't need one that will kill the engine (like for a race car) but
only to disconnect the battery,
they are pretty cheap almost anywhere.  I picked one up from JC Whitney (aka
JC Gyp-me) and it
turned out to be a Bosch unit with a big red key that looked just like the
expensive one with the 
generator cut-out that I put on my vintage race Midget.
--John Deikis