Common Wiring Faults
- Differentiate between causes of intermittent brake operation and directional pulling.
- Identify the relationship between wire color and brake pulling symptoms.
- Apply long-term repair strategies for terminal corrosion in electric brake systems.
- Digital Multimeter — Test for continuity in suspected broken wires and verify solid ground connections.
- Wire Strippers — Remove insulation from new wire sections when replacing broken leads or corroded terminals.
- Crimping Tool — Secure new connectors to wires after addressing the root cause of corrosion.
- Heat Shrink Tubing — Seal new connections to prevent the return of moisture-driven corrosion.
Intermittent brakes: broken wires, loose connections, or a faulty ground.
Brakes pull to one side: wrong magnet lead-wire color, broken wires or bad connections.
Fix the cause of corrosion, not just the corroded terminal. Fusing electric brakes is not recommended.
How It Works
Intermittent Brake Failure Points
Intermittent brake performance is typically traced to physical breaches in the circuit. Broken wires, loose mechanical connections, or a faulty ground point disrupt the flow of current intermittently as the trailer moves or vibrates.
Directional Pulling Logic
When brakes pull to one side, the electrical delivery is uneven. This is often caused by using the wrong magnet lead-wire color on one side, or by localized broken wires and bad connections that increase resistance on only one side of the axle.
Root Cause Remediation
Simply cleaning or replacing a corroded terminal is insufficient for a professional repair. The technician must identify and fix the underlying cause of the corrosion to prevent recurrence and ensure circuit integrity.
Diagnostic Chart
| Symptom | Check | Spec / Expected | Likely cause & fix |
|---|---|---|---|
| Intermittent brakes | Inspect for broken wires, loose connections, or a faulty ground. | Per the applicable manual | Mechanical vibration or strain causing temporary opens in the circuit. Basis: Dexter 600-8K Axle Service Manual |
| Brakes pull to one side | Verify magnet lead-wire colors and inspect for broken wires or bad connections. | Per the applicable manual | Incorrect wiring color or localized circuit degradation creating unequal braking force. Basis: Dexter 600-8K Axle Service Manual |
| Corroded terminals | Identify the environmental or physical source of moisture/contamination. | Fix the cause of corrosion, not just the corroded terminal. | Exposure to elements or poor sealing allowing chemical degradation of the metal. Basis: Dexter 600-8K Axle Service Manual |
At the Bay: Diagnose the Case
CASE 1 / 3
Intermittent brakes
- Test
- Compare
- Correct
Select the next check
Basis: Dexter 600-8K Axle Service Manual. A likely cause is a hypothesis; confirm it with the applicable service procedure before repair.
Common Bay Mistakes
- ✕ Installing fuses in the electric brake circuit.
- ✕ Replacing a corroded terminal without identifying the moisture source.
- ✕ Assuming all magnet lead-wires are interchangeable regardless of color.
- ✕ Overlooking the ground connection when troubleshooting intermittent operation.
- ✕ Ignoring loose connections that appear visually intact but lack mechanical tension.
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 600-8K Axle Service Manual — Troubleshooting chart