7-Way and 9-Way Color Codes
- Identify circuit assignments for 7-way and 9-way Dexter standard connectors.
- Verify the integrity of the common ground circuit as the primary step in electrical troubleshooting.
- Distinguish between primary lighting, electric brake, battery charge, and auxiliary circuits based on wire color codes.
- Digital Multimeter — Test for +12 V at the Black wire (Terminal #4) and verify ground continuity at Terminal #1.
- Test Light — Quickly verify presence of power on Stop/Turn terminals (#5 and #6) and Tail lights (#3).
- Terminal Cleaning Tool — Ensure clean contact points on the 7-way or 9-way plug to prevent high resistance ground faults.
- Contact Cleaner — Remove oxidation from terminals to ensure the White #1 common ground maintains a low-resistance path.
Most electrical faults are grounds. Terminal #1 (white) is the common ground for every circuit — verify it first.
How It Works
The Ground Priority
Most electrical faults are grounds. Terminal #1 (white) is the common ground for every circuit. Because all other functions rely on this single return path, it must be verified first before diagnosing individual circuit failures.
Standard Circuit Color Coding
Dexter utilizes specific colors to isolate functions: White for ground, Blue for brakes, Green for tail/running lights, Black for battery charging, Red and Brown for stop/turn signals, and Yellow for auxiliary. Adhering to this standard prevents cross-wiring safety systems like brakes with auxiliary loads.
Expansion to 9-Way Systems
The 9-way configuration retains the standard 7-way assignments but adds Terminal #8 (Grey) and Terminal #9 (Orange) as additional auxiliary circuits to support increased trailer functionality without overloading existing circuits.
Terminal / wire / circuit
| #1 White | Common ground |
| #2 Blue | Electric brakes |
| #3 Green | Tail, running & license lights |
| #4 Black | Battery charge (+12 V) |
| #5 Red | Stop & left turn |
| #6 Brown | Stop & right turn |
| #7 Yellow | Auxiliary circuit |
| #8 Grey (9-way) | Auxiliary circuit |
| #9 Orange (9-way) | Auxiliary circuit |
Diagnostic Chart
| Symptom | Check | Spec / Expected | Likely cause & fix |
|---|---|---|---|
| Total loss of all trailer electrical functions. | Test Terminal #1 (White) for continuity to the trailer frame and tow vehicle ground. | Common ground | Open circuit or poor connection at Terminal #1, which serves as the common ground for every circuit. Basis: Dexter Typical Trailer Wiring (2-09) |
| Electric brakes fail to engage when the controller is activated. | Verify power output at Terminal #2. | Blue wire / Electric brakes | Wiring fault in the Blue circuit or disconnected terminal at the plug. Basis: Dexter Typical Trailer Wiring (2-09) |
| Trailer battery does not charge while towing. | Measure voltage at Terminal #4 while the tow vehicle engine is running. | Black wire / Battery charge (+12 V) | Blown fuse in tow vehicle or break in the Black wire circuit. Basis: Dexter Typical Trailer Wiring (2-09) |
| Tail lights and license plate lights are inoperative. | Check for voltage at Terminal #3 with tow vehicle lights on. | Green wire / Tail, running & license lights | Fault in the Green wire circuit or failed bulb/connection at the license plate light. Basis: Dexter Typical Trailer Wiring (2-09) |
| Right turn signal works but Left turn signal does not. | Compare voltage at Terminal #5 (Red) against Terminal #6 (Brown). | Terminal #5 Red (Left) / Terminal #6 Brown (Right) | Open circuit in the Red wire path or specific terminal corrosion. Basis: Dexter Typical Trailer Wiring (2-09) |
At the Bay: Diagnose the Case
CASE 1 / 5
Total loss of all trailer electrical functions.
- Test
- Compare
- Correct
Select the next check
Basis: Dexter Typical Trailer Wiring (2-09). A likely cause is a hypothesis; confirm it with the applicable service procedure before repair.
Common Bay Mistakes
- ✕ Troubleshooting individual light bulbs before verifying the #1 White common ground.
- ✕ Confusing the Red wire (Left Stop/Turn) with the Brown wire (Right Stop/Turn).
- ✕ Assuming the Yellow wire is for turn signals when it is designated as an Auxiliary circuit.
- ✕ Neglecting to check the additional Grey (#8) and Orange (#9) wires on 9-way systems.
- ✕ Misidentifying the Black wire (+12V Battery Charge) as a ground wire.
Quick Check
Practice only — not scored.
Hands-on: Test Bench Practice
Symptom: Healthy trailer. Learn what good readings look like.
Tap a point to place the red probe.
Good system: ~12.6 V at pins, 3.2 Ω across a 12×2-inch magnet (unplugged), 3.0 A per magnet at 12 V full gain, and at least 10.5 V at the magnet — the chart values from the axle manuals.
Hands-on: Shop Test Equipment
IPA #9107B Electric Brake Force Meter
Plugs into the truck's 7-way socket on a 25 ft cable; simulates a trailer load and shows controller output on 10 blue LEDs
🛠 Equip your bay for this test →Symptom: Customer wants the truck checked before buying a trailer.
Spec limits used
- 1–10, each 1.0–1.5 V — Gain LEDs (IPA #9107B manual, p.5)
- 15 s — Max time holding brake pedal (IPA #9107B manual, p.4)
- set-up step 5 — Connect the 9-pin only after the engine is running (IPA #9107B manual, p.3)
- hold brake pedal during ECU detection — 2016–2017 'Trailer Connected' not shown (IPA #9107B manual, p.3)
- faulty brake control module or relay — ECU light never lights on a vehicle with a controller (IPA #9107B manual, p.5)
Simulated readings for practice. Always follow the manufacturer's procedure and values on a real trailer.
Hands-on: Wire-Trace Overlay
Pin 2 · Blue
Electric brakes
- Left and right brake magnets
- Breakaway switch output
Check points
- Two brakes draw about 6.0 A (3.0 A per magnet) at 12 V full gain.
- Unplugged: 3.2 Ω per magnet; at least 10.5 V at each magnet under load.
Common failures
- Open magnet: about half the expected current and a pull to one side.
- Shorted magnet: very low resistance and controller overload.
- Wire chafed where it drops to the axle.
Colors shown are the most common RV harness colors; makers vary — always verify against the trailer's wiring diagram.
Source: Dexter Typical Trailer Wiring (2-09) — 1