One thing to watch out for is you don't want to test a small ignition module to see how long of a spark you can get it to put out. That long spark causes the high voltage side of the coil to generate a really high voltage level. The extra high voltage tears down the coil wire insulation and shorts it out. They use simple varnish coated wire inside of the coil and that varnish is not intended to have a huge dialectric reistance to it. With modern automobile engines unplugging a spark plug wire or coil (usually the coil is right on top of the spark plug now) while the engine is running will promptly destroy the coil. A long time ago when I was in high school we used to hook up ignition coils and run them off a 12v battery and see how good of a spark we could get, and some coils did really good, but it did damage them and rendered them unusable in a car. You only want to generate sparks with the spark plug gap set properly.