Wiring Harness For Trailer Brakes | etrailer Electronic controller activates electric or electric-over-hydraulic trailer brakes with a preset intensity when you apply the brakes in your vehicle. Power output and braking aggressiveness remove the plug at the end of the integrated wiring harness. Electric Brake Wiring Harness | etrailer Install a 4-way flat on your vehicle with this splice-in harness. Powered converter connects directly to battery to reduce strain on wiring. Potted, SMT construction boosts water and vibration. This converter is a circuit-protected, battery-powered unit that bypasses the electrical routes that are used by a basic wiring harness. As a result, there is virtually no draw on your tail light circuits.