What do I need to do my electrical system in my dart.

Bewy said
If the battery is going to be in the trunk, you do NOT need to run a separate bat [-] wire to the front of the car. Just adding unnecessary extra weight. Iron/steel has 7 times more resistance than copper. That means if you had 7 pieces of steel connected in parallel, the resistance would equal one piece of copper with the same CSA & length. The car body will have less resistance than one piece of copper battery cable.

I disagree, these cars are not machined from a single billet of steel. There's paint, seam sealer, crud and rust between every panel. You're basically relying on the spot welds at that point.