The positive
Something is on drawing power from the battery. Always connect the positive cable first and the negative cable last.
schematic drawing
Then something is turned on and drawing current.
The term "schematic" comes from the greek word "schema" which means "drawing".
The drawing of an electrical circuit is called a.............= schematic drawing.
schematic
That is called "Negative Space", and it's just as important to the layout of a drawing as any positive (drawn) space.
Schematic or drawing showing the layout of components.
Remove the negative cable over night. If it does not hold a charge, the battery has a dead cell and needs replacing. If it does hold a charge but will not when the negative cable is connected you have something on that is drawing power from the battery. Some light or a relay is stuck.
Haynes
Disconnect the negative cable and connect (insert) an ammeter between the battery and the battery cable. Remove the fuses one by one and see which causes the current draw to drop.
You can find an exploded schematic view drawing of a 2003 Dodge truck front end online at places like Ram ForumZ and Diesel Place. You can also find this expanded version of the schematic on Diesel Truck Resource online.