One of the questions we hear all the time from diesel owners is, “Do I need one EMP Shield or two if my truck has dual batteries?” It’s a fair question, because when people open the hood of a diesel truck and see two batteries, the first assumption is usually that the vehicle must be running on a 24-volt system. In most cases, though, that’s not how diesel pickups and equipment are designed. Even with two batteries under the hood, the vast majority of diesel vehicles still operate on a 12-volt system, which means only one EMP Shield is needed.
What confuses many people is the way those batteries are wired. Most dual-battery diesel setups are wired in parallel, not in series. That distinction matters. When batteries are wired in parallel, the voltage stays at 12 volts while the available amperage increases. In simple terms, the truck gains more starting power without increasing system voltage. Both batteries work together, discharge together, and recharge together as one combined system. Even though there are two separate batteries physically installed in the truck, electrically they operate like one large 12-volt battery.
Because the system remains 12 volts, only one EMP Shield is required for protection. Since both batteries operate as a single electrical system, one properly installed shield protects the entire vehicle. While most diesel pickups use parallel-wired 12-volt systems, some commercial trucks, military vehicles, and specialized equipment may use 24-volt electrical systems. This is one of the most common misunderstandings we help customers with, and we are always happy to answer questions to make sure people fully understand how their vehicle operates before installation.
Although the batteries function together, one battery is usually considered the “primary” battery based on the truck’s wiring layout. Battery placement varies by make and model. On Ford Power Stroke trucks, the primary battery is typically on the passenger side, closest to the alternator, fuse box, and factory charging connections. On Ram Cummins trucks, the primary battery is typically on the drivers side. That said, this can vary depending on the generation and configuration of the truck. Most of the vehicle’s electronics tie directly into this battery, which makes it the ideal location for installing the EMP Shield. The secondary battery mainly exists to provide additional cold cranking amperage during startup.
Since EMP protection works best when installed as close to the electronics being protected as possible, we recommend installing the shield on the primary battery rather than the secondary battery. This placement gives the unit the most direct connection to the vehicle’s main electrical system. Even though the secondary battery contributes to starting power, it is not the central hub for the truck’s electronics and charging system.
The installation process itself is the same on a diesel vehicle as it is on a gas-powered vehicle. EMP Shield uses a simple three-wire installation. The red wire connects to the positive battery terminal, the black wire connects to the negative battery terminal, and the green wire connects to the metal frame or chassis of the vehicle. One important detail people sometimes overlook is the placement of that green ground wire.
The green wire should never be installed under the same grounding lug used by the battery’s factory negative cable. Doing so can create a ground loop, which may reduce the effectiveness of the shield or cause issues with the indicator light. Instead, the green wire should be attached to its own dedicated grounding point on the metal frame or chassis, as far away from the factory ground location as possible. In some cases, paint may need to be sanded or buffed away to ensure a clean metal-to-metal connection.
We also recommend leaving the wiring at its factory length rather than trimming excess wire. Any extra length can simply be bundled neatly and secured with zip ties for a cleaner install. After installation, the green indicator light on the EMP Shield should illuminate. This confirms the unit has power from the 12-volt system and that the ground connection is solid. If the green light does not come on, the most common issue is an improper ground connection.
Once the wiring is complete, the final step is mounting the unit securely in the engine bay. Each vehicle model includes heavy-duty Velcro designed to keep the shield firmly in place. Before attaching the Velcro, the mounting surface should be cleaned thoroughly with rubbing alcohol and allowed to dry completely. Choosing a flat mounting area helps the adhesive bond evenly and securely. Once installed properly, the unit will remain secure even during rough driving or off-road use.
At EMP Shield, we take pride in helping customers understand both the product and the installation process. We know that diesel electrical systems can seem confusing at first, especially with dual-battery setups, and we are always happy to assist with questions or installation guidance. Our goal is to make sure every customer feels confident that their vehicle or equipment is properly protected.
