How To Connect Battery Wires. Then connect the battery. If the battery has been removed from the vehicle you should connect a jumper cable or insulated battery cable at least 24 inches 60 cm long to the grounded post.
Connect a connector cable to the positive terminal of battery 2 and to the negative - terminal of battery 3. Then connect the battery. Connect the negative battery cable to the engine block where you took it off.
Connect the positive cable to the solenoid relay or starter.
If you have two wires coming out straight of the junction box skip this step. Then connect the battery. If you have two wires coming out straight of the junction box skip this step. The wires used to connect the batteries will be the longest and the highest-rated wires in your boat.
