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Fixing That Dead Battery Problem

We Diagnose an Electrical Draw and Install Painless Performance’s Dual-Battery Isolator on Our ’06 Dodge Ram 3500

John Lehenbauer
Mar 30, 2016
Photographers: John Lehenbauer
For the sake of fully understanding this tech project, imagine your truck being parked for a couple of weeks, and when you finally try to start the engine, there’s absolutely no response. Why? Because the battery is completely dead. At some point, this probably happens to just about everyone who owns a vehicle.
The Truck Trend Network’s rigs are definitely not immune. The 5.9L Cummins-powered ’06 Dodge Ram 3500 that tows the group’s promotions trailer to different events and shows typically remains parked for very long periods of time. And, of course, when it’s time to use the truck, its dual batteries are completely discharged.

So, what’s causing the premature death of both cells? Is the problem somewhere in the factory electrical system or in one of the truck’s aftermarket accessories (lights, winch, and so on)? To find the cause for the draw on the batteries, we need to do some investigating.

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This is the Truck Trend Network’s ’06 Dodge Ram 3500. The 24-valve, 5.9L Cummins-powered dualie is used by Diesel Power and other brands for hauling the group’s promotions trailer to shows and events throughout the United States.

For those not familiar with amp draw, it’s the total amount of amperes an electrical component uses. An example is an interior light that uses one amp or a driving light that uses three amps. Normally, when a truck’s engine and powered accessories are shut off, there shouldn’t be more than approximately 0.1 amp of draw on the battery. In newer rigs, that 0.1 amp comes from the memory backup for such things as the radio and engine-management computer.
Finding an electrical draw on a newer vehicle can be a daunting task, but not impossible. Even when you have zeroed in on the circuit that’s causing the problem, it can be difficult to pinpoint exactly where “open” in that circuit is. Sometimes it is easier and more cost effective to let a professional at a dealership or shop fix the problem, as they are more familiar with the systems and know what to look for.
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If you’re doing this yourself, a good, digital multimeter is needed. With all stock and aftermarket electrical components in the truck turned to the “off” position, the instrument is set at 10 amps (DC) and used for bridging the truck’s negative battery cable (which must be disconnected for the draw test) and the battery’s negative post. After completing the circuit with the multimeter, we recorded a 3.85-amp draw, which is indicative of headlights or a dome light being left on. By process of elimination, pulling fuses one by one is one of the best methods of individualizing each circuit until the problem is found. Our rig’s heavy draw, in a circuit called the Ignition Off Draw (IOD), was found and then identified using the owner’s manual. This circuit normally has a continuous load, but that draw is much smaller than our 3.85-amp reading was. While the manual also gives a short description of the IOD’s uses, our effort to try to locate the exact problem in the circuit was unsuccessful.
Ultimately, the tow rig will be sent to the dealer to have the draw repaired. To help alleviate the dead-battery problem until we get the Dodge Ram to authorized service, we’re installing a Painless Performance Products 250-amp Dual Battery Current Control System (PN 40103), a selectable isolator that will separate the truck’s two batteries during the long periods when it’s not being used and ensure that if one of the batteries is drained down, the other cell will have enough power to start the engine.
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A good, digital multimeter set to 10 amps (DC) is the only instrument necessary for investigating parasitic draw in a vehicle’s electrical system. With our tow vehicle’s batteries, lights, and accessories switched off or disconnected (including the dome and underhood lights), the first test yielded a 3.60-amp draw on the battery. Notice how the multimeter is used to complete the circuit (bridging the battery’s negative post and the terminal on the negative cable). Fuses remain intact for this test.

The following photos and captions highlight our efforts to pinpoint the draw on our Dodge Ram 3500’s batteries and our installation of the Painless Performance Products Dual Battery Current Control System. The kit includes everything needed (except 2/0 gauge battery cable, ring connectors, and shrink tubing) for a clean installation that can be accomplished in about three hours, using basic handtools.
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The test leads are connected with a piece of electrical tape and a jumper wire to maintain a constant reading while testing. The amp draw is a little higher here.
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Even though all accessories are disconnected, we also completely cut power to the fuse box under the hood.
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After pulling and replacing every fuse, the Ignition Off Drain (IOD) circuit proved to be the cause of a 3.85-amp draw, which dropped to 0.19 amps with the IOD fuse pulled.
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Here is the complete Painless Performance Products 250-amp Waterproof Dual Battery Current Control System. The kit includes step-by-step instructions and almost everything needed for a clean installation.
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We had to purchase 4 feet of 2/0 gauge battery cable, ring connectors, and some shrink tube from the local auto parts store to complete the project. Although we made custom cables for our Dodge Ram 3500 application, premade lines of different lengths and sizes can be purchased at most auto parts stores. The battery-cable size depends on the application. Diesel trucks like the Dodge Ram tend to use larger cables. This 2/0 cable runs from the starter to the isolator solenoid.
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This spot on the inner fender (near the driver-side battery) is an ideal location for mounting the isolator solenoid, as it allows us to use an existing bolt for one side of the solenoid’s mounting bracket. An existing hole in the engine bay is perfect for securing the other side of the bracket.
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Once the isolator solenoid is installed, disconnect the three factory power cables (primary battery/starter, ignition, and secondary battery) that will now be attached to the isolator.
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The two battery cables are installed on the isolator solenoid. We’re leaving the nuts loose for now.
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This wire and the main battery cable are connected to the isolator solenoid post that’s linked to the starter. The ignition wire is placed inside the split loom, which is then taped and is ready to be reconnected to the starter.
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When securing power cables to the isolator solenoid, it’s important to do so in a manner that will allow the lines to be neatly routed through the engine compartment and passed into the cabin.
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With the battery cables and isolator solenoid in place, we move inside the cab to install the mode-controller switch. The plastic panel is pulled off the lower dash on the driver side, and the wires are routed through the dash backing plate. A hole in the plastic is then drilled to facilitate mounting the switch. Wiring for the mode-controller switch is then passed through the firewall and out to the isolator solenoid.
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Two holes must be drilled for the system’s two LED lights
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The LEDs are connected to the correct wires coming from the mode-controller switch, and then the black wire is attached to a good ground.
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Once the lights and the ground are connected, the dash is reassembled.
When linking the mode-controller switch and isolator solenoid, the yellow wire is connected to the small post and the brown wire gets tied to the auxiliary battery-cable stud using the provided inline fuse. Using a test light, the fuse panel is probed to help find a circuit that is hot when the key is in the “On” position. The mode-controller switch’s blue wire is tapped into this fuse.
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With everything properly routed and secured, it’s now time to test the dual-battery isolator system.
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Painless Performance Products
Ft. Worth, TX 76105



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