Upfitting for a New Generation of Emergency Vehicles

(Source: Marek/stock.adobe.com)

Published April 30, 2026

Today's patrol cars are not just simple transport assets. As a result of digital technology, these vehicles act more like mobile command and response units. From secure communications to mobile data terminals that are wirelessly connected to headquarters, they are very different from patrol cars of the past. Emergency vehicles are not delivered from the factory with these features already integrated, though. The mission-specific equipment is added later, in a process known as upfitting.

Upfitting involves taking a vehicle directly from the manufacturer and equipping it with the systems required for operational service. Before the introduction of mobile electronics, upfitting meant installing lights, sirens, and radios, along with the associated switching and power distribution. The task was largely electrical, connecting equipment to the vehicle's 12V system using the existing harnessing. This blog details how the upfitting task has become a far more complex integration process due to additional networked, software-defined systems, and considers new solutions to these new demands.

From Standard Vehicle to Operational Platform

The vehicles used by emergency services usually begin as standard production models. They are often upgraded for the demanding duties of their future role, meaning they are fitted with high-capacity alternators and heavy-duty suspension. This is the chassis that is delivered to the upfitter.

Each department has distinct needs when upfitting a production vehicle for its specific service. Urban police forces may require extensive in-car video systems and constant access to centralized databases. Highway patrol units may prioritize communications range and high-visibility lighting. Fire, rescue, and EMS vehicles may need to include medical devices, detection systems, or additional computing equipment.

Radios, sirens, and light bars are still central, but are now joined by wireless routers, cameras, and charging docks for body-worn systems. These devices must function reliably under high vibration, in harsh weather, and during prolonged idle periods.

The increased load of technology places greater demands on the electrical system into which it is integrated. Power distribution must support continuous loads while protecting sensitive electronics. The hardware used in upfitting must allow departments to tailor their vehicles without redesigning the entire platform (Figure 1) Components must also be readily available, so vehicles do not sit out of service while waiting for parts. Upfitters work within tight service windows, which makes component standardization a logistical and technical requirement.

Figure 1: Modern emergency service vehicles that operate as mobile command and response platforms require standardized, modular power distribution hardware that supports continuous electrical loads, protects sensitive electronics, enables rapid customization without platform redesign, and minimizes downtime through readily available components compatible with tight service windows. (Source: Digital Storm/stock.adobe.com)

A broad scope of automotive-rated solutions is needed to help with different upfitting stages. Littelfuse offers products ranging from power delivery and circuit protection to rocker switches and in-cabin charging ports to support the demands of modern emergency vehicles. ZCASE^® fuses and protection devices help safeguard factory-fitted and upfitted wiring in 12V and 48V systems.

Precise low current fuses and durable high current fuses mounted in sealed fuse holders and power distribution modules, designed for harsh environments. Sealed continuous duty relays provide dependable control of high-current loads and support the long shifts common in emergency vehicles. Switches, switch modules, and in-cabin power solutions enable practical integration of auxiliary systems into the latest architectures.

Changes in the Automotive Industry

Vehicle manufacturers are moving away from large, centralized wiring harnesses and toward zonal architectures. Instead of routing individual circuits throughout the vehicle, power and data are managed through localized control units connected by high-speed networks. This reduces harness weight and can improve packaging efficiency, but it also alters how additional equipment must be integrated.

Upfitters do not just work with isolated circuits. These designs require careful analysis and disciplined installation strategies to add auxiliary equipment without disrupting existing systems. Power distribution is also changing. While 12V systems are still common across the automotive industry, many manufacturers are adopting 48V architectures to meet growing electrical demands. Increasing supply voltage allows equivalent power transfer at lower current, reducing conductor size and resistive losses. A significant benefit of this shift is that the reduced weight of thinner conductors positively impacts the range of electric and hybrid vehicles.

A vehicle that uses a 48V system may still need to provide 12V feeds for legacy systems. Components must be selected with voltage ratings and switching characteristics for these new demands. Acceptable design and installation practices for 12V systems can introduce risk in mixed-voltage environments. As such, protection and switching devices must be rated appropriately when higher-voltage subsystems coexist with sensitive data electronics within the same vehicle.

Electrification and High-Voltage Considerations

Emergency departments worldwide are adopting electric and hybrid vehicles,^[1] with some declaring goals to move away from fossil fuels.^[2] This change will affect the upfitting process. In conventional powertrains, the alternator and 12V battery provided a familiar and predictable source of power. In hybrid electric vehicles (HEVs) and battery electric vehicles (EVs), the energy source is the high-voltage battery pack, with DC-DC converters required to supply power to lower-voltage systems.

The power needs of integrated equipment impact the capabilities of EVs. Extended operation of lights, communications equipment, and onboard electronics reduces range, particularly for vehicles that are expected to be at incident scenes for long periods.

In automotive applications, DC systems with voltages above 60V are often regarded as hazardous. Working around these systems requires specific training and strict separation between high-voltage and low-voltage circuits in order to maintain operator safety. Upfitting now requires coordination across power distribution, network architecture, and safety.

As HEVs and EVs become more common in emergency fleets, upfitters need components that support modular and scalable installations. Littelfuse designs components that are tested for use in modern vehicle platforms, with features including compact design, standardized footprints, and clear derating guidance to help reduce delays during fleet builds.

Conclusion

Emergency vehicles have become mobile technology hubs, and the upfitting process now plays a defining role in ensuring that these platforms are ready for real-world demands. As power systems shift toward zonal architectures, mixed-voltage distribution, and electrified drivetrains, upfitters must integrate communications hardware, safety electronics, and mission-critical devices without compromising reliability or vehicle performance. This requires components that are robust and automotive-rated, as well as adaptable to the wide variety of fleet requirements.

Littelfuse supports this evolution with an extensive portfolio designed for every stage of the upfitting workflow—from high-capacity fuses and protection devices that safeguard increasingly complex power architectures to sealed relays, DC contactors, rocker switches, and in-cabin charging ports that bring functionality and durability to daily operations. By providing components engineered for continuous duty, modular integration, and mixed-voltage environments, Littelfuse helps ensure that today’s emergency vehicles can meet the expectations of modern field operations.

As emergency fleets continue adopting hybrid and electric platforms, the need for dependable, scalable, and fleet-ready solutions will only grow. Upfitters, engineers, and fleet managers can rely on Littelfuse to deliver the circuit protection, power management, and user-interface components required to build vehicles that remain operational—no matter the mission, environment, or technological change ahead.

[1]https://www.nyc.gov/site/dcas/news/009-25/dcas-fdny-30-all-electric-vehicles-including-city-s-first-ever-ev-paramedic-units
[2]https://www.england.nhs.uk/wp-content/uploads/2023/10/PRN00712_NHS-Net-Zero-Travel-and-Transport-Strategy.pdf

David Pike is well known across the interconnect industry for his passion and general geekiness. His online name is Connector Geek.