The existing mass cable remains, only a second one is built into it. Just as the first one is attached to the battery with connector and screw, the second point is a screw in the engine compartment, possibly on the other side of the already existing connection. Cable thickness approximately the same as the already existing one. Is it useful to install such a thing to exclude bad or worse-growing mass connections as well as possible and to give the current as much return connection as possible?