How to use Timing Light?

Having trouble getting my timing light to flash consistently. How exactly should I go about doing this?? The gun I am using has three connections, all clamps, two larger ones and one smaller one.

I am assuming that one of the clamps goes onto an ignition wire. Which one should it go to? Number 1, to the coil, doesn't matter??

Then I think the two larger ones will go to the positive and negative terminals on the battery. Is that right?

Thanks,

Mike