Wide-view mirror

Width marker lights make the outer contours of wide vehicles, bodies and attached components clearly visible. This signalling lighting is essential for night work, manoeuvring, passing on narrow roads and operation in rain, fog or dusty working environments. For MAN and Mercedes trucks, buses and vans, width marker lights are available as front, rear and side contour lights, often featuring LED technology or conventional incandescent bulbs. The correct width marker light must always be determined using the vehicle chassis number. Visual comparison, relying solely on the model type or lamp shape, is never sufficient, as connector design, wiring harness, homologation, voltage and mounting position may differ.

Width marker lights are used on, among others, MAN TGL, TGM, TGA, TGS, TGX and TG3, as well as Mercedes Atego, Axor, Actros, Arocs and Econic. Coaches and buses such as the MAN Lion’s City, Lion’s Coach, Mercedes Citaro, Intouro, Tourismo and Neoplan Cityliner or Tourliner also use specific contour lighting in body panels, roof edges or mirror arms. On vans, including the MAN TGE and Mercedes Sprinter, Vito and Vario, width marker lights may form part of the roof structure, load body or body extension.

Technically, a distinction is made between white front width marker lights, red rear width marker lights and amber side marker lights. The selected lamp must comply with the required ECE homologation, light colour, visibility angle and mounting height. In 24V systems used on trucks and buses, a 12V lamp must never be fitted as an alternative: overheating, immediate failure and damage to the lamp holder or electronic control system are real risks. LED units generally have lower power consumption, but require correct polarity and may trigger lamp monitoring warnings in certain vehicle configurations when the load does not match the expected circuit value.

The most common faults are complete lamp failure, flickering LED lighting, moisture or condensation in the lens, a cracked housing and oxidation of connector contacts. On vehicles with bodywork, damage is often caused by branches, loading and unloading operations, car washes or contact with loading bays. On older MAN F90, F2000, M2000 and L2000, or Mercedes LN, SK and Ecoliner vehicles, hardened cable insulation and corroded earth points are frequent causes. On newer vehicles, a fault may also be stored in the onboard computer as a lamp failure or short circuit.

First check the relevant fuse, relay operation and fault codes of the lighting module. Then use a multimeter to measure the supply voltage directly at the lamp connector while the lights are switched on. In a 24V circuit, the measured voltage under load should be close to the onboard voltage; a significant voltage drop indicates contact resistance in cable terminals, connectors or earth connections. Next, test the earth connection using a voltage drop test between the lamp earth pin and the chassis. A high voltage drop indicates corrosion, a loose earth bolt or a broken wire.

Then inspect the wiring harness for chafing, particularly near mudguards, chassis pass-throughs, body supports and cab tilt points. In the case of LED width marker lights with intermittent failure, it is advisable to load the connector using a test lamp or current clamp: a voltage measurement without load may show an apparently correct supply despite a damaged conductor.

Replace a width marker light when the lens is damaged, the housing allows moisture ingress, the light output is insufficient or the integrated LED module is found to be defective. Always clean the connector pins and inspect the sealing rings before installation. Use cables with the correct conductor cross-section, sealed crimp connections and heat-resistant corrugated conduit where the wiring harness may rub against the chassis. Install the lamp flush and without stress; incorrect fitment can cause cracks in the plastic housing due to vibration.

A correct chassis number check and technical support during selection help prevent downtime caused by incorrect connectors, different mounting points or incompatible lamp monitoring.