Electric-Hydraulic Compatibility and Diagnostics
- Confirm controller compatibility with the installed actuator.
- Separate electrical supply faults from hydraulic response faults.
- Interpret breakaway-test results without generalizing actuator-specific wiring.
- Digital multimeter — Measure supply and breakaway-feed voltage at the terminals and under the conditions identified in the actuator instructions.
- Battery charger — Fully charge the breakaway battery before evaluating a nonrunning actuator.
- Brake bleeding kit — Remove trapped air from the actuator and brake circuits using the applicable bleeding procedure.
- Brake adjustment tool — Correct drum-brake clearance when drum brakes are fitted, following the brake manufacturer's instructions.
- Wire brush — Clean accessible ground-contact surfaces when directed by the service procedure.
- Basic hand tools — Access wiring connections and service ground fasteners without damaging terminals.
An electric-hydraulic actuator uses electrical control to supply pressurized brake fluid. Controller compatibility must be confirmed rather than assumed, because controller design changes can affect operation.
Slow response can come from air in the system, incorrect drum-brake clearance, undersized wiring, or controller adjustment. Rebleeding, correcting drum clearance, checking wire requirements, and following the controller adjustment instructions address different possible causes rather than treating them as interchangeable repairs.
For an actuator that does not run with ignition on and the brake pedal depressed, check wiring against its schematic and examine the ground connection. Dexter specifies a 12–13 V supply check between the documented black and white wires with ignition on and brakes unapplied; wire assignments and values vary by maker.
The documented breakaway test separates likely actuator problems from controller or interconnecting-wiring problems. Running and building pressure points toward the controller or its wiring, while running without pressure points toward a defective actuator solenoid valve. A nonrunning unit requires a charged breakaway battery and the specified voltage checks before the replacement decision.
How It Works
Compatibility comes before adjustment
An electric-hydraulic actuator converts an electrical braking command into pressurized brake fluid, so controller compatibility must be confirmed for the installed equipment rather than inferred from connector fit. Controller design changes can affect operation; verify compatibility and follow the applicable adjustment instructions before treating poor response as actuator failure. For overly aggressive braking, reduce controller gain according to the instructions.
Similar delays can have different causes
Trapped air compresses under pressure, while excessive drum-brake clearance requires additional movement before the shoes engage; either can delay braking response. Undersized supply wiring can cause voltage drop under load, and controller adjustment can alter the braking command. Rebleeding, correcting drum clearance, checking wire requirements, and adjusting the controller address distinct causes and are not interchangeable repairs.
Breakaway testing isolates fault paths
The documented breakaway test helps separate likely actuator faults from controller or interconnecting-wiring faults by distinguishing motor operation from pressure generation. Running and building pressure points toward the controller or its wiring, whereas running without pressure points toward a defective actuator solenoid valve. A nonrunning actuator requires a fully charged breakaway battery and the specified voltage checks before a replacement decision; do not leave the switch pulled for more than 2 minutes during any test step.
Step-by-Step Procedure
0/8 doneDexter electric-hydraulic test references; values vary by maker
| Unapplied supply check | 12–13 V between black and white wires with ignition on |
| Breakaway test duration limit | Do not leave the switch pulled for more than 2 minutes during any test step |
| Nonrunning-unit breakaway-feed check | Check for at least 12 V between white and yellow wires after fully charging the breakaway battery |
Diagnostic Chart
| Symptom | Check | Spec / Expected | Likely cause & fix |
|---|---|---|---|
| Braking responds slowly. | Confirm controller compatibility, rebleed the brakes and actuator, and correct drum clearance if applicable. Check supply-wire sizing and controller settings against the applicable instructions. | Use the installed equipment's bleeding, drum-clearance, wire-sizing, and controller-adjustment instructions; the lesson supplies no universal settings. | Possible trapped air, incorrect drum-brake clearance, undersized wiring, or controller adjustment. Basis: LDServiceOnline |
| Actuator does not run with ignition on and the brake pedal depressed. | Compare the wiring with the actuator schematic and examine the ground connection; clean or replace it as directed. For the documented Dexter supply check, release the brakes while leaving ignition on and measure between the identified black and white wires. | 12–13 V between black and white wires with ignition on; brakes must be unapplied for this supply check. Wire assignments and values vary by maker. | Possible wiring error, poor ground, or inadequate supply; no operation alone does not establish actuator failure. Basis: LDServiceOnline |
| Actuator runs during the documented breakaway test. | Determine whether the actuator builds pressure, rather than treating motor sound as proof of hydraulic operation. Follow the documented test procedure and restore the switch promptly. | Do not leave the switch pulled for more than 2 minutes during any test step. | Running with pressure points toward the controller or interconnecting wiring; running without pressure points toward a defective actuator solenoid valve. Basis: LDServiceOnline |
| Actuator does not run during the documented breakaway test. | Fully charge the breakaway battery, then perform the documented breakaway-feed voltage check before deciding whether replacement is justified. Confirm that the procedure and wire assignments apply to the installed actuator. | Check for at least 12 V between white and yellow wires after fully charging the breakaway battery. Do not leave the switch pulled for more than 2 minutes during any test step. | A discharged battery or inadequate breakaway feed must be addressed before concluding that the actuator is defective. Basis: LDServiceOnline |
At the Bay: Diagnose the Case
CASE 1 / 4
Braking responds slowly.
- Test
- Compare
- Correct
Select the next check
Basis: LDServiceOnline. A likely cause is a hypothesis; confirm it with the applicable service procedure before repair.
Common Bay Mistakes
- ✕ Assuming a controller is compatible because the connector fits.
- ✕ Using gain adjustment to mask air or incorrect drum clearance.
- ✕ Applying Dexter wire colors and test values to every actuator.
- ✕ Leaving the breakaway switch pulled beyond the documented test limit.
Quick Check
Practice only — not scored.
Plan the Service Sequence
Planning practice only. Follow the applicable manufacturer's instructions, employer safety program and qualified supervision on real equipment.
Plan the first action. Compare the service steps with the bay mistakes.
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: 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: LDServiceOnline — 29-31