Dual Battery (Gasoline)
WARNING: This page is about a different car, the 2002 Ford RV Cutaway, 2002 Ford Econoline, 2002 Ford E550 Super Duty, 2002 Ford E450 Super Duty, and 2002 Ford Cutaway. However, it is still accessible from the selected car via links, so may be relevant.
Disconnect primary battery negative cable. Remove ground bolt and pull secondary battery negative cable away from frame. Insulate secondary negative battery cable with non-conductive material.