Relays & accessories
In the electrical installation of a truck, semi-trailer or trailer, relays play a central role. They form the link between a low-power control signal and a high-power load circuit, enabling heavy consumers to be safely and reliably switched without placing the control component itself under high current load. For professional workshops, trailer builders, bodybuilders and transport companies with their own maintenance facility, a well-stocked range of relays and relay accessories is not a luxury but a necessity.
The Relays & Accessories category covers all components required for the correct switching, protection and mounting of electrical circuits in vehicles operating on both 12V and 24V DC systems. This includes a wide range of relay types, from compact micro-relays for light-duty applications to robust normally-open power relays for the most demanding conditions in heavy transport. The category also includes relay holders and combination holders with integrated fuse functions, ensuring that relays remain firmly and safely mounted in an environment with constant vibration and temperature fluctuations.
Within the relay subcategory for trucks and trailers, several variants are available, each with their own area of application. A switching relay trailer for 24V systems is used to control lighting, electric drives or safety systems on the trailer. A starter relay 24V with high switching current is designed for driving starter motors in heavy transport, buses and construction machinery. The 4-pin and 5-pin versions offer flexibility in the switching circuit: a 5-pin relay with changeover contact makes it possible to control both a normally-open and a normally-closed circuit from a single component, saving space in the electrical enclosure.
Bosch relay HGV products are particularly popular in this segment due to their mechanical reliability, precise switching characteristics and proven durability over a high number of switching cycles. Whether it is a relay truck 24V for heavy vehicles or a 12V version for lighter applications in vans and trailers, the Bosch quality standard is a reference widely recognised in professional vehicle electronics. Bosch relays are compatible with standard relay bases and holders, simplifying interchangeability in existing installations.
In addition to standard switching relays, isolation relays also fall within this category. An isolation relay is used to electrically separate two battery circuits, allowing a secondary battery to be charged while the starter battery is protected against backflow and discharge. This is a common application in trucks and trailers where refrigeration units, tail lifts or other consumers are powered from a separate circuit.
A specific consideration when using relay truck 24V components is the choice of switching configuration. A normally-open relay activates the load when the coil is energised, while a changeover relay with configuration 87/87b can drive two separate circuits depending on the coil state. The choice between these versions depends on the requirements of the specific application and vehicle type.
The relay holder subcategory is just as essential as the relays themselves. In a vehicle environment with constant vibration, mechanical shocks and temperature fluctuations, a stable mounting base for every relay is indispensable. A relay holder 24V keeps the relay in position and prevents poor contacts or failure due to mechanical stress. For installations where circuit protection is also required, a relay holder with integrated fuse function offers a compact and organised solution that saves both space and wiring time.
The complete range in this category has been compiled with the day-to-day practice of the truck and trailer industry in mind. From professional garages maintaining multiple vehicles per day to trailer builders fully wiring new semi-trailers: the right relays and matching holders are the foundation of a reliable electrical installation in heavy transport.