Just to get an Idea of what you are doing. you will be attaching a piece of metal in the vice to be welded? you are hoping to install a battery interrupter in order to avoid disconnecting the battery every time? if you attach the material in the vice and attach your ground clamp directly to the material as close to the weld as you can, there should not be any reason why the current would travel to the front of the car to where your battery is located. you will always want to disconnect the battery when welding on any vehicle, in fact, I usually pull the battery completely out for piece of mind. Understand that you do not want to be pulling the heavy battery out of the vehicle every time you want to weld something on the back of your tailgate. in that case, disconnect both your ground cable and your positive cable and forget the battery interrupter. electricity is not something that you take the easy route with in my opinion. good luck. also, look out for that gas tank. hehe!
