Etownlax,
The simplest way of doing this is with a relay. Set up the relay coil to be fed through a Normally Closed (NC) pair of contacts.
To do this:
1) Connect the common from the relay contacts to one end of the coil.
2) Connect the other end of the coil to the negative on your battery.
3) Connect the positive of the battery to the NC (Normally Closed) contact.
The relay will now start buzzing. They don't last a long time doing this, but it is fun to try.
Now connect the primary terminals of your transformer in parallel with the relay coil.
Measure the voltage on the secondary terminals of your transformer.
Voila!
