[Bill G]

In series with the battery. Either side of the battery will work, however, there has been a lot said of the benefits to putting it on the positive (ground) side. Really super simple as far as what connects where. The hard part is where to physically put the switch in a convenient place and the resulting routing of the rather heavy gauge wires to/from the switch. A lot has been written and discussed on that, you might get a lot of hits if you used the search function and sifted through the discussions. One thing is certain. Unless you have a show car for judging, it is certain that you DO need a battery shut-off switch.