The answer is on your trailer, not in a weight table. If it has electric or electric-over-hydraulic brakes, you need a controller, because those brakes have no other way to operate. If it has surge brakes, you do not, and fitting one would do nothing at all.
The second question is the one that catches people out, and it is not about weight either. Brake controllers are rated by axle count, and the ratings differ more than the prices suggest — of the five we hold records for, one stops at two axles, two at three, and two at four. A triple-axle trailer rules one out. A four-axle trailer rules out three, including the most expensive.
Step 1 of 3
What brakes does the trailer have?
This is the question that decides everything else, and it is the one most often guessed at. Look at the trailer, not at the tow vehicle.
The answer
Do you need a controller?
—
Controllers rated for this trailer
Tekonsha Brakeman IV Time-Delay Trailer Brake Controller
Up to 4 axles · 30 A · None — a fixed time ramp, not a measurement
Check price at Tekonsha(opens in a new tab)Tekonsha Primus IQ Proportional Trailer Brake Controller
Up to 3 axles · 30 A ·
Check price at Tekonsha(opens in a new tab)Tekonsha Prodigy P3 Proportional Trailer Brake Controller
Up to 4 axles · 30 A · Inertial sensor — axis count not published
Check price at Tekonsha(opens in a new tab)CURT Echo Mobile Trailer Brake Controller, 7-Way Bluetooth
Up to 2 axles · 30 A · Triple-axis accelerometer
Check price at CURT(opens in a new tab)REDARC Tow-Pro Elite V3 Electric Trailer Brake Controller
Up to 3 axles · 25 A ·
Check price at REDARC Electronics(opens in a new tab)What actually decides it
Three things, in this order. None of them is the trailer’s weight.
1. What brakes the trailer has. Electric drum brakes have an electromagnet in each drum, energised by the controller through the 7-way connector — no controller, no braking. Electric over hydraulic uses the same signal to drive a pump on the trailer. Surge brakes need nothing: the coupler slides as the trailer pushes forward under braking and actuates a master cylinder mechanically.
2. How many axles. Two brakes per axle, and the controller has to be rated for the count. This rules out more controllers than anything else.
3. Whether the tow vehicle already has one. A factory integrated controller does the job. Replacing it is a choice about adjustment and modes, not a requirement — and note that at least one plug-in controller disables an existing one rather than working alongside it.
The arithmetic, and where it comes from
Trailer brake current is one of the few numbers in towing that a manufacturer publishes plainly. Dexter’s Magnet Amperes Chart gives it per magnet:
| Brake size | Amps per magnet | Magnet ohms |
|---|---|---|
| 7 in × 1¼ in | 2.5 A | 3.9 Ω |
| 10 in × 1½ in | 3.0 A | 3.2 Ω |
| 10 in × 2¼ in | 3.0 A | 3.2 Ω |
| 12 in × 2 in | 3.0 A | 3.2 Ω |
| 12¼ in × 2½ in | 3.0 A | 3.2 Ω |
| 12¼ in × 3⅜ in | 3.0 A | 3.2 Ω |
Two brakes per axle, so the system draw is axles × 2 × amps per magnet. A twin-axle trailer on 10-inch brakes is 12 A; a triple-axle is 18 A.
One honest note about the eight-brake case. Dexter’s published totals stop at six brakes — it prints 5/6 A for two, 10/12 A for four and 15/18 A for six. The roughly 24 A figure for a four-axle trailer is Dexter’s per-magnet number multiplied out, not something Dexter prints, and the checker above says so when it applies.
That matters in one place: REDARC’s Tow-Pro Elite is rated at 25 A on a 12V vehicle, against 30 A for the Tekonsha units. Eight 12-inch brakes at 3.0 A would sit within a couple of amps of that ceiling — and the Tow-Pro Elite is rated to three axles anyway, so its axle limit and its current limit tell you the same thing. That the two agree is a good sign that both figures are real.
When you need nothing at all
The checker refuses to recommend anything in two cases, and both are worth stating plainly because a page that sells a controller to everyone is not answering the question.
Surge brakes. A controller has nothing to drive. Some surge actuators do take a 12V feed, but only for a reverse lock-out solenoid so the brakes do not apply when you back up — that is not braking, and it is not what a controller operates.
No brakes on the trailer. A controller cannot create braking that is not fitted. If the trailer is heavy enough to want brakes, the fix is brakes, and then a controller.
The five controllers, by rating
| Model | Axles | Current | Sensing | Price | Buy |
|---|---|---|---|---|---|
| Tekonsha Prodigy P3 | 1–4 axles | 30 A | Inertial sensor — axis count not published | $$ | Check price(opens in a new tab) |
| Tekonsha Brakeman IV | 1–4 axles | 30 A | None — a fixed time ramp, not a measurement | $ | Check price(opens in a new tab) |
| Tekonsha Primus IQ | 1–3 axles | 30 A | — | $$ | Check price(opens in a new tab) |
| REDARC Tow-Pro Elite V3 | 3 axles maximum. The manual's specification table gives "Max. Trailer Axles — 3 Axles" and its safety section states the unit "is suitable for trailers with electric brakes up to three axles" | 25 A on a 12V vehicle (30 A on 24V), 18 A nominal draw | — | $$$$ | Check price(opens in a new tab) |
| CURT Echo | 1–2 axles | — | Triple-axis accelerometer | $$$ | Check price(opens in a new tab) |
Read the axle column first. The pattern worth noticing is that it does not follow price: the cheapest controller here covers four axles, and the most expensive covers three.
The legal question, and what this page will not do
Where trailer brakes are required by law, something has to operate them, so the controller requirement follows the brake requirement. The threshold is a state question, this page does not compute it for your state, and you should be sceptical of any tool that claims to.
One verified example, so the shape of the rule is clear: Iowa Code 321.430 requires every travel trailer or trailer coach of 3,000 lb gross weight or more intended for human habitation to have brakes the driver can apply from the cab, plus a separate auxiliary means of applying them. Note how low 3,000 lb is — that is a small trailer.
Thresholds elsewhere differ, and we have not verified all fifty states. Check your own state’s vehicle code. And treat your trailer manufacturer’s requirements as binding regardless of what the law permits — the law sets a floor, not a specification.
Download the US Letter or A4 brake-gain worksheet, or print it from your browser. It separates the P3’s manual-knob test from the Echo’s brake-pedal test, with six trial rows and loaded/empty settings records. The checker above does not calculate gain; these fields stay blank for your road-test results.
Brake gain road-test worksheet
Blank log for electric trailer brakes using the P3 or Echo 51180 procedures below. Other controllers and hydraulic setups need their own manuals. Trailer weight alone cannot give you a gain setting.
One portrait page. Fill in the log only while parked.
Date: __________ Controller: ____________________ Trailer/load: ____________________
Tekonsha Prodigy P3 (90195)
Electric-brake setup, before setting Boost: warm trailer brakes with light manual braking for about 1/4 mile at 45 mph, as the P3 manual specifies. With the engine running, start power at 6.0. At 25 mph, fully apply the manual knob. Confirm the result with several low-speed brake-pedal stops.
CURT Echo Mobile (51180)
Complete installation, pairing and calibration first. At about 25 mph, use the vehicle brake pedal to set max output. Then test sensitivity with the pedal: increase it for a slow response or reduce it for harsh braking. Sensitivity does not change manual-override output. Follow the Echo manual; P3 settings do not transfer.
- Choose a clear test area with enough stopping room, on dry, level pavement. Read the controller and brake manuals first; record your current load below.
- Use only the matching procedure above. Park before writing or changing settings. For Echo adjustments: transmission in park or neutral, parking brake set, foot off the pedal and manual control released.
- After each run, reduce power/max output if wheels lock; increase it if braking is weak. Repeat for firm braking without skidding. A missing brake response needs troubleshooting, not endless gain increases.
- Confirm smooth pedal stops. Retest when the load, towing setup or road/weather conditions change; an old setting is only a record, not a guarantee.
| # | Power / output | Speed | Brake response | Next change |
|---|---|---|---|---|
| 1 | mph | locked / firm / weak / none | up / down / keep / inspect | |
| 2 | mph | locked / firm / weak / none | up / down / keep / inspect | |
| 3 | mph | locked / firm / weak / none | up / down / keep / inspect | |
| 4 | mph | locked / firm / weak / none | up / down / keep / inspect | |
| 5 | mph | locked / firm / weak / none | up / down / keep / inspect | |
| 6 | mph | locked / firm / weak / none | up / down / keep / inspect |
Final settings — trailer loaded
Power/output: ____________________
Boost/sensitivity: __________________
Date / weight (lb): _________________
Final settings — trailer empty
Power/output: ____________________
Boost/sensitivity: __________________
Date / weight (lb): _________________
Do not keep a setting that locks the wheels. Skidding can destabilize the rig. If braking stays weak, absent or erratic, stop the test and use the manual's fault checks or a qualified brake technician. Gain cannot repair a brake or wiring fault.
Procedure references checked 4 October 2026. P3 warm-up and starting power apply to that model only. This is a summary of the linked manuals; RVTrove has not road-tested these controllers. Product verification dates are unchanged.
rvtrove.com/towing/do-i-need-a-brake-controller/
Which one, once it fits
Fits the most trailers
Tekonsha Prodigy P3
Four axles, 30 A, electric-over-hydraulic on a menu setting. The fewest ways to be ruled out.
Cheapest that still covers four axles
Tekonsha Brakeman IV
Same axle and amp rating as the P3 and also does electric-over-hydraulic — you give up proportional braking, not compatibility.
If the module has to hide
REDARC Tow-Pro Elite V3
Mounts in any orientation with only a knob showing. Three axles maximum, so check that first.
Being rated for the trailer is the floor, not the recommendation. What separates these once they all fit is how they decide braking effort and where they can be mounted — covered in proportional vs time-delay, and for the two most cross-shopped units in Tekonsha P3 vs REDARC Tow-Pro Elite. All five are written up side by side in best trailer brake controllers, organised by what rules each one out rather than as a countdown.
Questions worth answering
Do I need a brake controller?
If your trailer has electric or electric-over-hydraulic brakes, yes — those brakes have no way to operate without one. If it has surge (hydraulic) brakes, no, and fitting one would achieve nothing, because surge brakes are actuated by the trailer pushing against the coupler as you slow. If it has no brakes at all, a controller does nothing either. The question is answered by looking at the trailer, not by weight.
How do I tell what kind of brakes my trailer has?
Look behind a wheel and at the coupler. A wire running into the backing plate behind the wheel means electric drum brakes. A coupler at the front that slides in and out on the A-frame, with no wiring running back to the axles, means surge. A small pump and fluid reservoir mounted on the A-frame means electric over hydraulic. If none of that is conclusive, the trailer's own manual or VIN plate will say.
How much current do trailer brakes draw?
Dexter publishes it per magnet, and it is the same across almost the whole range: 2.5 A per magnet on 7-inch brakes, and 3.0 A on every 10-inch and 12-inch size it lists. Two brakes per axle, so a twin-axle trailer on 10-inch brakes draws about 12 A with all magnets energised and a triple-axle draws about 18 A. Dexter's published table stops at six brakes; an eight-brake trailer works out at about 24 A on the same per-magnet figure.
Does the number of axles change which controller I can buy?
More than anything else does, and it is the most-missed constraint in the category. Of the five controllers we hold records for, one is rated to two axles, two to three axles and two to four. A triple-axle trailer rules out one of them; a four-axle trailer rules out three, including the most expensive. Check the axle rating before the reviews.
Can I use a brake controller if my truck already has one built in?
You do not need to. A factory integrated controller does the same job, and replacing it is a preference rather than a requirement — usually for finer adjustment or a second braking mode. Note that some plug-in controllers are not additive: CURT states that "an existing aftermarket or factory brake controller will not function if Echo brake controller is installed", so it replaces rather than supplements.
What size brake controller do I need?
"Size" here means two separate ratings, not one. The axle rating says how many brakes it is designed to drive; the current rating says how many amps it can pass. Both have to clear your trailer. The current rating is rarely the binding one on an RV — 30 A covers eight brakes — but the axle rating binds often, and the two are published as separate figures for a reason.
Does electric over hydraulic need a special controller?
It needs one that supports it, and support is not implied by price or by control type. Tekonsha's Prodigy P3 has an explicit Electric-or-Hydraulic menu setting. Its Primus IQ, which costs more than its time-delay units, is documented as having "not been tested for the use on electric over hydraulic brakes". REDARC's Tow-Pro Elite supports it but its manual notes that "most Electric/Hydraulic systems require a separate 12V power feed for the hydraulic pump". Check the specific model and your actuator's own requirements.
Is a brake controller required by law?
Where trailer brakes are required, something has to operate them, so in practice the two go together — but the threshold is a state question and this page does not answer it for your state. As one verified example, Iowa Code 321.430 requires a travel trailer of 3,000 lb gross or more to have brakes the driver can apply from the cab. Thresholds elsewhere differ. Check your own state's vehicle code, and treat your trailer manufacturer's requirements as binding regardless of what the law permits.
What gain should I set it to?
There is no number anyone can give you, and be wary of any page that offers one. Gain depends on the trailer, its load, the condition of its brakes, the surface and the tow vehicle, which is why every manufacturer publishes a road-test procedure instead of a formula. The P3 and Echo manuals both use a dry, level paved surface at about 25 mph, but the P3 uses its manual knob and the Echo uses the vehicle's brake pedal. Follow your model's procedure and adjust while parked. The downloadable worksheet separates those instructions and provides a blank test log.