Navigating chassis electrical system challenges

From an NTEA member We are an upfitter experiencing regular issues handling newer chassis electrical systems, especially with lighting flashing too fast or working for a little while and then stopping. As these problems consistently occur with different chassis we work on, is the cause and solution similar across all OEMs? Although it’s hard to generalize electrical system issues across makes and models, there are some common causes of fast-flashing turn signals and other non-functioning circuit challenges. Modern chassis electrical systems utilize modules (small on-board computers) to control and monitor current, voltage and resistance levels on various circuits (such as lighting) in order to protect system components and report problems. These modules deactivate circuits and generate diagnostic codes when an issue is detected. Although OEMs have different names for the modules, a customary feature of chassis electrical architecture is individual lighting circuits for the left and right sides of a vehicle. This allows driver and passenger side stop/turn/tail lamps and other circuits to be monitored separately. The electrical modules will respond when referenced voltage or amperage levels are detected above or below the individual circuit thresholds set by chassis manufacturers. Accordingly, total circuit amperage draw must remain within these threshold limits after adding lamps or other devices. Regardless of chassis brand, an electrical load analysis will help determine what can be added to a given circuit. However, the similarities end there. To find out how much reserve capacity exists, you’ll need to review applicable OEM body builder information. Ultimately, you’ll need to clarify whether or not the lights and components you are adding will allow the circuit to stay within the available current. Existing reserve current capacity or a maximum circuit total may be published. As other lights and components may be part of the original circuit, their loads will need to be subtracted from the maximum total to determine reserve capacity. Then, compare available levels to the additional load of the lighting and other components your customer requests. If the circuit load falls under the lower threshold, particularly for fast-flash issues with turn signals, adding resistance to the circuit may work as it has been a common solution across chassis makes. However, reprogramming modules to accept a new lower threshold is a more efficient solution and has become a widely available option. Conversely, when additional load exceeds reserve capacity, using a relay to control lamps or other devices is a cross-brand solution. The relatively low draw of the relay might fit within reserve capacity while the device itself may not. Other considerations All components added to a circuit will increase resistance. While individual items might be overlooked, resistance resulting from a combination of longer runs of lighter gauge wiring, switches, connectors, etc., can add up and reduce extra capacity. LED lights draw less current than incandescent bulbs. This can be a positive feature, but may cause current levels to drop under the lower threshold of what a lighting module is programmed to expect — especially for turn signal circuits and trigger bulb outage detection. Avoid the fuse rating as a limit when assessing circuit load as the threshold against which modules react will be less than the amount of current for which a circuit is fused. This helps guard against damage during load spikes. Instead, look for maximum continuous load or a similar notation when reviewing body builder information for circuit capacities. If you can’t find a maximum circuit load value, it’s helpful to note chassis OEMs recommend about 80 percent of the fused rating as a typical maximum load for individual circuits. This doesn’t mean a module uses this specific threshold value, but it provides a good estimate.

Navigating chassis electrical system challenges

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