Trailer Brake Controller: What It Is and How to Choose One

A trailer brake controller is the electronic box that tells your trailer’s electric brakes when and how hard to apply, making towing heavy loads safer and legally compliant in NZ. Without one, stopping distances blow out, tow-vehicle brakes overheat, and a routine police check can end in fines or worse. In short, this modest device stands between you and the chaos of a runaway two-tonne caravan.

In the next few minutes you’ll gain a working grasp of how controllers function, the legal thresholds that apply across New Zealand, the different technologies on offer—from budget timed units to wireless proportional models—and a simple five-step method to match the right unit to your rig. We’ll round things off with installation tips, maintenance hacks, and a quick-fire FAQ so you can hit the road confident your trailer will stop exactly when you do. Let’s get braking under control—starting with the basics.

Understanding Trailer Brake Controllers

Think of a trailer brake controller as the translator between your right foot and the brakes bolted to the trailer’s axles. When you press the vehicle pedal, the unit converts that stop-light signal into metered voltage that fires the trailer’s electric magnets (or powers an electric-over-hydraulic pump). The harder you brake, the harder it tells the trailer to bite.

Most Kiwi rigs run straight electric drum brakes; heavier caravans and many boat trailers use electric-over-hydraulic disc setups for extra grunt. In both cases the controller sits up front: dash-mounted box, discreet remote knob, or a fully trailer-mounted wireless unit. Placement doesn’t change its job—without it, your trailer’s service brakes simply won’t activate.

Core Components and Terminology

• Control head – the visible module or knob you adjust.
• Accelerometer / inertia sensor – measures deceleration so proportional units can mirror vehicle braking force.
• Gain dial – sets maximum brake voltage; fine-tuning for different loads.
• Manual override – trigger on the controller that lets you apply trailer brakes independently to correct sway.
• Wiring harness – dedicated loom linking controller to battery, stop-light circuit, earth and the blue brake wire.
• Trailer plug – 7-pin or 12-pin connector carrying the brake output to the trailer.
• GTM (Gross Trailer Mass) – the weight resting on the wheels, crucial for legality.
• Brake latency – delay between vehicle braking and trailer response; lower is better.

How the Signal Flows

1. Foot presses vehicle brake pedal.
2. Brake-light circuit goes live.
3. Controller brain wakes, reads deceleration or timer.
4. Calculates required voltage (0 – 12 V).
5. Sends power down the blue brake wire through the 7/12-pin plug.
6. Trailer brake magnets engage or hydraulic pump pressurises callipers.
7. Tow-vehicle and trailer slow together, sharing the load.

Do You Really Need One?

NZ Transport Agency rules state any trailer over 2,000 kg GTM must have service brakes controllable from the driver’s seat. Ignore that and you risk fines, a failed WoF and voided insurance. Safety is the kicker: tests show a 2.5-tonne boat trailer can add more than 20 m to the 100 km/h stopping distance without a controller. Fit a quality proportional unit and you regain factory-like braking feel, protect your ute’s pads, and keep the constabulary—and your passengers—happy.

Legal Requirements and Safety Standards in New Zealand

Before you worry about fancy features, make sure the controller you’re eyeing keeps you on the right side of the law. The New Zealand Transport Agency (NZTA) sets clear braking thresholds based on Gross Trailer Mass (GTM). If the trailer can’t meet them, it won’t pass a Warrant of Fitness and your insurer can walk away after a claim.

Failing to meet the above can earn on-the-spot fines, defect notices, or worse—charges for careless use if an accident follows. NZ Police frequently check braking compliance at boat ramps and summer holiday roadblocks, so skipping a controller is a false economy.

ADR, ECE and NZS Compliance Labels

Controllers sold here should display either ADR 38/05 (Australia), ECE R13, or NZS 5467 markings. Look for a laser-etched code on the housing or packaging. These standards verify that the unit can deliver consistent current, self-diagnose faults and survive Kiwi levels of dust and moisture. No marking? Walk away—the WoF inspector certainly will.

Towing on Steep Grades and Gravel Roads

New Zealand’s terrain amplifies braking loads: think Remutaka, Arthurs Pass or a corrugated forestry track to the hut. Dial a slightly higher gain before descending long grades, then back it off on loose gravel to avoid wheel lock-up. A quick 10-second tweak can save your tyres—and your nerves—without ever touching the foot brake harder than normal.

Types of Trailer Brake Controllers Explained

Not every trailer brake controller is built the same, and picking the wrong style can leave you with jerky stops or a hefty bill for gear you never use. All units fall into four broad camps, each aimed at a different towing pattern and budget. Get a handle on the differences below before you swipe the card.

Timed (Time-Delayed) Controllers

A timed controller starts a countdown the moment it sees the brake-light signal, ramping output at a fixed rate until it hits the gain you set.

• Pros: cheapest option (often under NZ $200), simple two-wire splice into the stop-light circuit, tolerant of odd mounting angles.
• Cons: brakes the same on gravel, tarmac or ice, so it can grab or fade; requires constant gain tweaks as load varies.
  Best for the occasional jet-ski run or furniture trailer under roughly 1 800 kg where outright smoothness isn’t critical.

Proportional (Inertia or Motion-Sensing) Controllers

Inside a proportional unit lives an accelerometer that feels vehicle deceleration and matches trailer brake force in real time. The result is seamless stopping and reduced pad wear.

• Ideal on NZ’s undulating highways and stop-start city traffic.
• Models like the Redarc Tow-Pro Elite or Tekonsha P3 self-level and store multiple trailer profiles.
  You’ll pay NZ $350–$550 but the drive feels factory-smooth from day one.

Wireless and Trailer-Mounted Controllers

Here the brain sits on the draw-bar, powered by the trailer’s break-away battery. A Bluetooth remote or dash knob handles the adjustments.

• Flexibility: swap tow vehicles in minutes—handy for lease utes or shared fleet use.
• Legal note: NZTA accepts them so long as the driver has immediate control (keep the remote in reach).
  Popular picks include Elecbrakes and the locally supplied Credo kit. Budget around NZ $400–$650.

Electric-Over-Hydraulic (EOH) Compatible Units

If your boat trailer runs disc brakes or your caravan tips 3 t, chances are it’s EOH. These pumps draw more current and need a sealed controller able to pulse up to 20–30 A. Check the spec sheet—many premium proportional units have an EOH mode, cheaper timed boxes rarely do.

Quick Decision Grid

Still unsure? Jot down what matters most, match it to the grid above, and you’ll zero in on the right controller faster than you can say “brake check”.

Key Features and Specs to Compare Before Buying

The catalogue blurb for a trailer brake controller can read like alphabet soup—volts, amps, ADR, boost curves. Strip away the jargon and only a handful of specs truly decide whether a unit will play nicely with your rig, your budget and New Zealand law. Run through the checklist below before you tap “Add to Cart”.

• Brake capacity / axle rating – The maximum amperage the controller can supply. Match it to the trailer’s combined brake magnet or hydraulic pump draw, not just GTM.
• System voltage – Most leisure vehicles are 12 V; some light trucks and imported buses are 24 V. A dual-voltage controller saves headaches if you swap tow vehicles.
• Gain range and resolution – Finer steps (e.g. 0.1 V increments) make it easier to dial in the sweet spot between lock-up and lazy braking.
• Boost or load presets – One-touch buttons that add extra bite when you’re fully loaded or tackling a steep descent.
• Manual override – A squeeze lever or push button to apply trailer brakes independently for sway control and ramp launches.
• User interface – Big, glove-friendly knobs beat tiny flush buttons on corrugated gravel.
• Diagnostics and fault codes – Built-in LED or LCD read-outs quickly tell you if a wire has chafed or a magnet has failed.
• Compliance markings – ADR 38/05, ECE R13 or NZS 5467 engraved on the housing = WoF peace of mind.
• Wiring style – Plug-and-play looms with OEM connectors speed DIY jobs; hard-wire pigtails are cheaper but add labour.

Handy Print-Out Checklist

1. Confirm tow vehicle voltage (12 V/24 V)
2. Check trailer current draw vs controller capacity
3. Look for ADR / ECE / NZS label
4. Decide on gain adjustment style (dial vs knob)
5. Note wiring kit inclusions and extra costs

Advanced Features Worth Paying For

• Self-levelling accelerometer keeps proportional units accurate even if you change tyre size or hitch height.
• Multiple trailer memory stores gain settings for the boat, caravan and works trailer separately.
• Reverse-polarity and short-circuit protection protects both vehicle fuses and the pricey hydraulic pump on EOH setups.
• In-cab remote knob (e.g. Redarc Tow-Pro) lets you hide the control box and keep the dash tidy.
• Sway-mitigation and hill-hold algorithms add micro-pulses to keep the trailer tracking straight on windy Canterbury plains or while crawling up the Takaka Hill.

Cost vs Value in the NZ Market

Expect to spend:

• NZ $120–$200 for basic timed units—fine for light, occasional towing but limited resale appeal.
• NZ $350–$550 for quality proportional models—sweet spot for most family utes and caravans.
• NZ $400–$650 for wireless or EOH-ready gear—premium price, yet cheaper than swapping hard-wired controllers between multiple vehicles.

Factor installation: an auto-sparky charges around NZ $120–$180 per hour, plus $40–$80 in wiring sundries. Spending a little more up front on a plug-and-play kit or self-calibrating model often saves that amount—and a few swear words—down the road.

Step-by-Step Guide to Choosing the Right Controller for Your Rig

Skip the guesswork by working through the five-step checklist below. It takes you from a bare-bones look at your trailer brakes to a concrete purchase decision that suits both your wallet and New Zealand’s legal framework. Jot answers as you go; by Step 5 you’ll know exactly which trailer brake controller to order and how you’ll get it fitted.

Step 1: Confirm Trailer and Tow-Vehicle Brake Type

Pop the trailer’s compliance plate or owner’s manual: does it list electric drum, electric-over-hydraulic disc, or—gulp—“no service brakes”? Do the same for the tow-vehicle wiring (12 V or 24 V stop-light feed, factory brake-controller plug?). Matching brake technology is non-negotiable; a time-delay box won’t drive an EOH pump, and a 24 V truck will fry a 12 V controller.

Step 2: Calculate GTM and Payload Variations

Legal class determines controller size. Run the maths:

GTM = ATM – Tow Ball Mass

Example: a 2 800 kg caravan with 250 kg on the ball leaves 2 550 kg GTM—well over the 2 000 kg threshold, so driver-controlled service brakes are mandatory. If you occasionally haul extra water or bikes, add that weight now to keep a safety margin.

Step 3: Match Controller Type to Towing Frequency and Terrain

Ask yourself:

• Weekend missions to the boat ramp? Timed unit may suffice.
• Monthly South Island road-trips with alpine descents? Go proportional.
• Multiple drivers swapping fleet utes? Wireless trailer-mounted wins.

Use the quick decision grid from the previous section and circle the column that best fits your routine.

Step 4: Check Vehicle Electrical System Compatibility

Modern utes run CAN-bus networks that hate rogue current draws. Look for:

• Factory pre-wired brake-controller socket behind the dash
• Spare 30 A fuse location
• 6 mm² wiring pathway to the trailer plug

If none exist, budget extra for wiring looms or an auto-sparky’s time.

Step 5: Decide on DIY or Professional Installation

DIY saves cash but voids warranties if you botch it. Pick pro install when:

• Vehicle is under dealership warranty
• You lack crimping tools or multimeter skills
• You need a WoF sign-off fast

Labour typically runs NZ $120–NZ $180/hr; many installers offer a package price that includes calibration and a quick road test—money well spent if it keeps you straight and legal on the highway.

Installation, Setup and Calibration Basics

Fitting a trailer brake controller isn’t wizardry, but it does demand tidy wiring and a methodical test drive. The golden rules: follow the manufacturer’s wiring diagram to the letter, protect every connection from water and vibration, and finish with a proper gain calibration on flat tarmac. If you feel out of your depth, hand the job to an auto-sparky—labour is still cheaper than replacing a fried ECU.

Wiring and Mounting Essentials

A typical proportional controller needs four hard wires:

• +12 V battery feed through a 30 A auto-reset breaker
• Chassis earth on clean, paint-free metal
• Brake-light trigger (cold side of the pedal switch or CAN-friendly adaptor)
• Blue brake output to the trailer plug

Route the loom inside split conduit, keeping it clear of exhausts and sharp chassis edges. Use 6 mm² cable for runs up to six metres; step up to 8 mm² on long motorhomes. Mount the control box within the angle tolerance stated in the manual—usually ±5° of level for proportional units. Remote-knob models can hide under the dash, leaving just a neat rotary dial in view.

First-Time Calibration and Gain Setting

1. Load the trailer as you would for travel.
2. On a dry, straight road, reach 30 km/h and squeeze the manual override until the rig slows firmly without locking wheels.
3. If the trailer drags, back gain off in small steps; if it feels lazy, bump it up.
4. Repeat on gravel or wet seal—reduce gain by 5–10 % for slippery surfaces.

Most modern controllers store this setting, but re-check whenever load or tyre size changes.

Common Installation Mistakes to Avoid

• Skipping an independent earth, causing voltage drop and weak brakes
• Crimping with household pliers—use ratchet crimpers and heat-shrink for every join
• Sharing the battery feed with caravan auxiliaries (fridges, chargers)
• Ignoring cable protection where the loom passes through the tub or chassis rail
• Forgetting to seal the trailer plug with dielectric grease, leading to green corrosion and phantom fault codes

Address these traps up front and your trailer brake controller will deliver years of hassle-free stopping power.

Maintenance and On-Road Troubleshooting

A trailer brake controller is only as good as the wiring and hardware that support it. Spending five minutes every month with a torch can save hours stranded on the hard-shoulder or at the boat ramp.

Monthly DIY Inspection

• Run your hand along the wiring loom from the tow-bar to the chassis clip; look for chafed insulation or flattened conduit.
• Crack open the 7- or 12-pin plug; any green fuzz means corrosion—clean with contact cleaner and dab a smear of dielectric grease.
• Jack one trailer wheel clear of the ground, spin it and pull the manual override. You should feel a firm drag and hear the magnets hum; weak bite signals a worn magnet or low voltage.
• Measure brake magnet resistance with a multimeter (3–4 Ω each). Anything above 5 Ω points to a dying coil.

Reading Fault Codes

Most modern units flash or display simple two-letter codes:

Roadside Fixes That Work

Keep a micro kit under the seat: spare 30 A fuse, roll of insulation tape, zip-ties, contact cleaner and a pre-greased replacement plug. Nine times out of ten, reseating the earth or trimming back a crushed wire restores normal braking long enough to reach the next servo.

Special Care for Salt-Water Launches

Salt spray eats terminals fast. Rinse the trailer plug with fresh water after every launch, let it dry, then re-grease. Once a season, pop the drum covers, hose off salt crystals, and check the backing plate for rust pitting that can snag the shoes and overload the controller.

Frequently Asked Questions About Trailer Brake Controllers

Below are the questions our shop staff hear almost daily. Each answer is short enough to screenshot yet detailed enough to keep you on the right side of the NZ Transport Agency and basic physics. Bookmark this lot and you’ll have roadside confidence at your fingertips.

Do I really need a trailer brake controller?

If your trailer’s GTM exceeds 2 000 kg the law says driver-controlled service brakes are mandatory, and that means a controller. Even under the limit, a controller shortens stopping distances, reduces tow-vehicle brake wear and makes downhill descents markedly smoother.

What happens if you tow without one?

The trailer brakes simply don’t engage. Expect up to 20 m longer stops from 100 km/h, overheated pads on the ute, and a high chance of insurance refusal after a crash. Police can also issue on-the-spot fines or defect your rig at roadside checks.

Are trailer-mounted units legal in NZ?

Yes—provided the driver can adjust or manually apply them from the cab. Wireless systems like Elecbrakes or Credo meet this requirement through a dash remote or phone app, and they still need the usual break-away battery and compliance labelling.

How do I wire a controller to a 7-pin/12-pin plug?

Run a dedicated 6 mm² blue wire from the controller’s brake-output terminal to the trailer socket (pin 5 on NZ 7-pin flat, pin 2 on most 12-pin). Add a 30 A breaker on the battery feed, solid chassis earth, and tap the cold side of the brake-light switch.

Can I use one controller for multiple trailers?

Absolutely. Proportional units with memory store separate gain settings for each trailer, while wireless trailer-mounted controllers move with the load. Just recalibrate gain whenever trailer weight or surface conditions change to keep braking balanced and compliant.

Ready to Tow with Confidence

Choosing a quality trailer brake controller isn’t rocket science: know your trailer’s weight, pick the controller style that matches your driving habits, insist on ADR / ECE compliance, and wire it up cleanly or pay a pro. Do that and you’ll enjoy factory-smooth stopping, cooler tow-vehicle brakes, and zero heart-in-mouth moments when the road drops away in front of you.

Timed, proportional, wireless or EOH—each has a sweet spot, but every one of them beats towing a heavy, unbraked load. Follow the five-step framework from this guide, run the gain test in an empty car-park, and keep a monthly eye on plugs and wiring. The result is legal peace of mind and a rig that feels planted no matter how steep the hill or how twisty the gravel.

Ready to kit out your setup? Check out the full range of Trojan controllers, wiring kits and accessories at Action Outdoors or drop into our Auckland store for hands-on advice and nationwide shipping.