FIELD GUIDE
A repeatable method for diagnosing dark, flickering, intermittent and incorrect indications without replacing good equipment by guesswork.
Published August 6, 2026 · GAOQIAO Traffic Technology
Start with a safe incident record
Record the intersection, approach, time, weather, signal group, controller alarm and the exact symptom before opening a cabinet. Secure the work area and follow the project isolation procedure. A clear record prevents a temporary communication fault from being mistaken for a failed signal head.
Use the symptom to narrow the search
| Symptom | First checks | Likely areas |
|---|---|---|
| Entire head dark | Cabinet output, fuse, connector seating | Power feed, harness, module |
| One colour dark | Output channel and colour lead | LED module, terminal, cable |
| Flicker or drop-out | Voltage under load, moisture, vibration | Loose crimp, water ingress, driver |
| Wrong indication | Phase mapping and terminal labels | Controller configuration or wiring |
Check power and controller interfaces
Qualified personnel should compare measured supply and output with the approved project values, not a generic nominal value, following the approved safe test procedure. Confirm the controller phase plan, channel assignment and the status of any specified flash-transfer relay and conflict monitor. If the controller is operating correctly, safely isolate the field circuit before sectional cable testing under the approved procedure.
Inspect the field harness and signal head
Qualified personnel should inspect under the approved safe-work procedure, including isolation where required. Look for crushed cables, loose terminals, corrosion, damaged glands and incompletely locked connectors. Check the specified drip-loop and strain-relief arrangements. Inspect the module, lens, visor and seals for heat damage or condensation. Investigate the cause before selecting a compatible replacement subassembly, and retain removed parts for analysis where appropriate.
Close the job with an acceptance checklist
- Restore every colour and arrow/figure indication in the approved sequence.
- Confirm night dimming, flash mode and controller conflict monitoring.
- Photograph the repaired termination and record measured values.
- Update the spare-parts and maintenance log for the next visit.
When to request a configuration review
Escalate when the fault follows a controller change, a new cabinet, a tunnel interface or a non-standard indication. GAOQIAO can review the controller arrangement, signal head configuration and wiring information before a replacement is selected.
FAQs
Should I replace the whole signal head when one colour fails?
Usually no. Test the channel, harness and LED module first; replace the smallest failed assembly that meets the project requirements.
Why does a fault disappear after rain?
Intermittent moisture at a gland, connector or terminal can dry out and temporarily restore contact. Record the condition and inspect seals before it returns.