At first glance, it looks like what you have is an automotive continuity tester. A 12V light bulb in the handle will glow when you hook the alligator clip to any grounded surface and touch the pointed tip to a live wire. Very useful for checking out trailer wiring, but there are lots of other uses too. It is possible to replace the 12V light bulb with a small neon light and it will work as a spark tester, but be careful how you hold it. It may not be insulated enough to protect you from 30,000 volts or so. If it is, indeed, a sparkchecker, you should attach the alligator clip to ground and touch the tip to the sparkplug terminal.
Some test lights have a neon bulb in the handle to serve as a spark plug tester. Hard to tell from the picture. If it contains a small bulb, it's a 12 volt tester. If it contains a neon bulb, then it can be used as a spark tester.
Anyway, the clip goes to ground and the pointed probe goes to whatever you're testing. I have one that has a place to screw in the probe on both ends. If I screw the probe in on the handle end, then it connects to the neon buld and words as a spark tester. If I screw it into the normal end, it connects to a small 12 volt bulb and words as a normal test lamp.
Connect the clip to ground and put the probe on the spark plug terminal with the engine running. If its a regular test light, nothing will happen except you might kill the engine. If its in fact a spark tester, you'll see an orange neon flash every time the plug fires.
That is a TEST LIGHT not a spark tester:bonk: It has a 12 volt bulb and illuminates when a 12 volt circuit is connected. Clamp the alligator clip to the NEG side of your car battery and the long point to the positve side and whala illumination