The problem was likely that one of your connections was not good. Some people say that the last negative connection should be made to the chassis itself to reduce the posibility of explosion. There is some merit to this, but you can ignore it if it is a windy day. The advantage of the direct connection is that there is less resistance. The lead in top-post terminals is rather soft, and the teeth of the clamps can grip right in and make a great connection easily.

If you attach the calbes to the chassis, you have to make sure that the cables touch metal and not paint/grease/rust.