A traffic light wiring diagram maps every conductor, terminal and controller output. Learn to read the schematic, follow the common and switched conductors, and verify the work before power is applied.
Conductor schedule
| Circuit function | Required verification |
|---|---|
| Red, yellow and green signal outputs | Identify each output conductor by its terminal assignment and the approved wiring drawing; do not assume a regional insulation-colour convention. |
| Common or return conductor | Confirm the circuit topology, supply type and designated common terminal before connecting. A common conductor is not automatically a protective-earth conductor. |
| Protective earthing | Identify and connect protective earthing according to the applicable electrical rules and approved equipment drawings. Do not substitute it for a signal output. |
| Verification before energising | A qualified person should verify terminal labels, continuity and protective measures with the circuit safely isolated, using the approved test procedure. |
1. Why a wiring diagram matters
A current as-built wiring diagram documents how the signal system is connected and supports fault finding. Missing or incorrect drawings can contribute to wrong signal assignments, maintenance errors and disputes about installation responsibilities. Verify the wiring and configured monitoring against the approved design; a conflict monitor is not a substitute for this verification. Keep a protected printed copy inside the cabinet where required and a controlled digital as-built version for future maintenance and project records.
2. Anatomy of a signal head schematic
A schematic for a particular 3-aspect vehicle head may show red, yellow and green indications connected to separate switched outputs and a shared common. This is an example arrangement, not a universal connection rule. Confirm the actual common, supply, polarity where relevant and terminal labels from the model-specific diagram. Labels such as R, Y, G and C or COM must be interpreted using that diagram before connection.
A 4-aspect head may combine circular and arrow indications in different configurations. Obtain the approved diagram for the exact model and identify each controlled indication, output channel, conductor and permitted common connection. If an assembly includes a multi-colour arrow module, confirm how its colours are controlled rather than assuming one output per physical section. The cable schedule should identify every conductor by number, colour and function. Do not assume all 4-aspect heads use six outputs or share a common conductor.
3. Identify common and switched conductors from the approved wiring diagram
Some signal configurations use a shared conductor and a separate switched conductor for each indication. Confirm the selected controller and signal wiring diagrams, voltage and switching arrangement. A terminal labelled COM is not automatically neutral, and protective earth must not be used as a functional return conductor.
Select conductor functions, common-return capacity, polarity and protective earthing from the approved wiring diagram for the exact signal-head and controller versions. A common return must carry the applicable combined load. Do not substitute protective earth for a circuit return, and do not infer line or neutral switching from an AC voltage label. Qualified personnel must isolate the circuit and verify the electrical arrangement using the applicable safety procedure before connecting or servicing it.
4. Controller terminals and conflict monitoring
Check the controller’s approved terminal diagram to identify switched outputs and any common terminals; the output count alone does not define the physical terminal arrangement. Confirm whether the selected controller and cabinet include conflict monitoring, which circuits are monitored, and the approved response to a detected conflict. Do not assume that each output physically passes through a monitor or that every controller provides the same protection.
When reading the actual cabinet diagram, locate the output terminals, any fitted conflict monitor, detector inputs and each power supply. Their labels and layout depend on the cabinet design. Match the conductor schedule to the designated terminals and check the documented supply voltages and interfaces. Identify spare conductors explicitly and resolve unexplained connections against the approved drawing before commissioning. Example terminal names or accessory voltages must not replace the model-specific diagram.
5. Reading 4-aspect, arrow and pedestrian schematics
The number of signal sections does not, by itself, establish the required controller outputs. List every independently controlled colour or symbol and check its circuit against the selected product wiring diagram. Pedestrian push buttons are controller inputs; audible and tactile indicators may require additional interfaces. Confirm the output allocation, common-return arrangement and supply for pedestrian, bicycle and arrow indications rather than assuming a universal circuit count.
When reading combined schematics for vehicle, arrow and pedestrian heads on one pole, trace each head to its assigned controller outputs using the approved drawing. Check conductor identification and the intended indication before commissioning. Record and resolve any mismatch; do not assume that a visually plausible connection is correct.
6. Common wiring faults
If the approved diagram shows a shared common conductor, have a qualified technician investigate a possible break using the specified isolation and testing procedure.
7. Inspection and controlled commissioning
Before energising, qualified personnel should follow the approved commissioning procedure and traffic-management arrangements. Check conductor termination and labelling, continuity, insulation and protective bonding using methods appropriate to the equipment. Test the specified conflict-monitor and detector functions with compatible equipment. Verify each required indication and the approved sequence in a controlled test arrangement that cannot give conflicting instructions to live traffic. Record results against the acceptance criteria. If a test fails, isolate and correct the fault before commissioning.
Frequently asked questions
How do I read a traffic light wiring diagram?
Using the approved model-specific diagram and safe-work procedure, trace each conductor from the controller output panel to the signal head. Identify any permitted common conductor and the separately controlled indication conductors. Match each conductor colour and number to the cable schedule. Confirm that each indication is assigned to the correct output before commissioning.
What is the common conductor in a traffic signal?
A common terminal may be labelled COM or C, but its electrical function and polarity depend on the equipment circuit. Use the approved wiring diagram to identify the common connection and each switched indication conductor. Do not assume that common always means neutral, negative or a shared return, and never substitute protective earth for it.
Are traffic light wires colour-coded?
Confirm the project cable-identification scheme and applicable electrical rules before installing wiring. Project conventions must not be assumed to override mandatory conductor-identification requirements. Identify functions from approved diagrams rather than colour alone, and confirm available cable options with GAOQIAO for the selected specification.
How many wires does a 3-aspect traffic light need?
Select the cable’s conductor count, cross-sections and identification scheme from the approved wiring design and applicable electrical requirements. A regional label alone does not define a safe signal-to-colour mapping.
What is a conflict monitor?
A conflict monitor supervises defined cabinet conditions and initiates the configured response when a monitored fault is detected. The monitored conditions, fault latching, flashing or other fallback behavior and reset procedure depend on the selected equipment and approved cabinet design. Verify these functions using the manufacturer’s documentation and an approved controlled test; do not assume that every monitor detects every conflict or always produces the same intersection state.
Can I read a wiring diagram without electrical training?
The basics (conductor count, common vs switched, terminal labels) can be learned quickly, but final termination and commissioning should always be done by a qualified electrician following local electrical codes. Use the diagram as a reference, not a substitute for training.
How do I update an old diagram after a field change?
Mark up the as-built drawing with a red pen, then transfer the changes to a clean digital copy. Replace the laminated copy inside the cabinet. Update the master drawing held by the authority and the supplier. Never let field reality drift from the documented drawing.
Relevant GAOQIAO products
These public GAOQIAO catalogue pages are related to the guide. Open them for the representative description, then confirm the latest wiring schedule and configuration before ordering.
- Traffic signal controllers22-output and 56-output controllers with documented terminal layouts.
- 300 mm (12 inch) LED traffic lightsStandard 3-aspect, 4-aspect, arrow and pedestrian heads.
- Wired traffic signal controllers22-output and 56-output controllers matched to the cabinet terminal schedule.
- Traffic signal controller solutionsSelection guide for wired, wireless and solar controller systems.