Signalisation lights

Signal lamps ensure that other road users can identify a vehicle's direction of travel, braking deceleration, width and presence in good time. This lighting includes indicators, brake lights, rear lights, clearance lights, side marker lamps, outline marker lamps, reversing lights, rear fog lights and hazard warning lights. On trucks, buses and vans, these lighting functions are important not only for road safety, but also for legal type approval and technical inspection.

The correct specification varies greatly between vehicle series. A MAN TGL, TGM, TGS, TGX or TG3 may have different lamp housings, connectors, mounting points and CAN bus monitoring than older F90, F2000 or L2000 series. The same applies to the Mercedes Atego, Axor, Actros, Arocs, Econic, Sprinter, Vito, Citaro and Tourismo. MAN Lion’s City buses and Neoplan coaches also often use specific light units with different connector pin assignments, lens colours, LED modules or mounting positions. Therefore, always identify signal lamps using the vehicle's chassis number. Visual comparison or selection based on the model name alone is never sufficient.

Common fault symptoms include rapidly flashing indicators, a bulb warning on the dashboard, intermittent failure, moisture inside the lens, weak light output or a completely failed lighting function. In conventional lamp units, blown bulbs, corroded bulb holders and thermally deformed contact plates are typical causes. In LED signal lamps, internal LED segments, integrated control electronics or the housing seal may fail. An LED unit generally cannot be reliably repaired once moisture has penetrated the electronics.

Start diagnosis with a visual inspection of the lens, housing, rubber seals, connector housing and cable entry. Check for hairline cracks, condensation, green oxidation on connector pins and cable damage caused by vibration or rubbing against chassis or body components. Then use a multimeter to measure the supply voltage between positive and earth under load. In a 24V system, the voltage drop across supply or earth circuits must remain limited; a clearly lower voltage at the lamp unit indicates contact resistance in cable terminals, earth points, fuse holders or connectors.

On bulb systems, also measure the continuity of the earth connection and inspect the bulb holder for spring tension and heat damage. For LED units, preferably use a diagnostic tester to check fault codes, open-load warnings and short circuits to earth or positive. A test lamp as a load test is useful for distinguishing between a voltage measurement without power capacity and a circuit that can actually supply sufficient current. On vehicles with bulb monitoring, an incorrect wattage rating or a universal LED replacement can cause fault messages.

Replace a damaged signal lamp as a complete unit when the lens is cracked, the housing is no longer watertight, the reflector is damaged or the LED electronics are malfunctioning. Always use a unit with the correct ECE approval, lighting function, lens colour, connection configuration and IP sealing. For side marker lamps and clearance lights, ensure the correct cable outlet, centre-to-centre mounting distance and polarity of the LED connections.

Before installation, clean the connector pins and repair loose cables only using suitable crimp connections, sealing heat-shrink tubing and correct strain relief. After installation, check all functions: left/right indicator, brake light, rear light, hazard warning lights and any trailer output. Correct signalling operation not only prevents inspection failures and fines, but also reduces downtime caused by recurring electrical faults. Braem can provide support with technical identification based on the chassis number and parts of verified quality.