Dual Battery Wiring Diagram - 200 Amp Solenoid & Toggle Switch (Jump/Isolate)

This document is a hand-drawn/simple schematic wiring diagram for a dual battery setup in a vehicle. It shows a main battery and a secondary battery, both with grounded negative terminals, connected through a 200 Amp solenoid. A three-position toggle switch controls the solenoid with settings labeled On (Jump), Off (Isolated), and On (Normal). The switch receives power from the Crank/Run power circuit in the vehicle wiring harness. A 10 Amp fuse protects the small-gauge wire running to the secondary battery's positive terminal (used for the switch/solenoid control circuit). The solenoid's input side ties to the main battery's positive terminal via the 'Normal Positive Connection,' while the output side feeds the secondary battery. From this diagram a reader can learn how to wire an isolated dual-battery system that can (1) operate normally with the batteries joined when the engine is running, (2) isolate the secondary battery entirely, or (3) jump-start the vehicle from the secondary battery. The diagram is generic and does not state a specific year, make, or model, though it was uploaded to a 1986 Ford Bronco gallery and is applicable to such installations.