Use this article if…
- Your wheel controls work until your lights go on, then they stop.
- Your horn sounds on its own, or stays on.
- You've been told your module is blown and you want to check the supply first.
Quick answer
Fit a horn booster if your wheel controls work until you switch your parkers or headlights on. The module behind your wheel takes its power from the horn circuit, and on some vehicles that circuit won't hold voltage once your lights load it. The booster runs from behind your headunit receiver to the horn pin in your steering column and steadies the supply.
Problem
- Your wheel controls and your horn share one circuit, and that circuit is running out of voltage.
Symptoms
- Your volume and track buttons work in daylight and stop once your lights are on.
- Your controls come back when you switch your lights off.
- Your horn sounds on its own, or sticks on.
- Your horn is weak or takes a firm press.
Cause
- Your controls run on horn power. The transmitter behind your wheel draws its supply from the horn circuit. No horn feed means no buttons, whatever your headunit is doing.
- Your lights share the load. On some vehicles the voltage reaching that module drops once your parkers and headlights are on, and the module stops responding before anything else shows a fault.
- A starved module looks like a dead one. The same shortage can leave your horn sounding on its own or staying on, which reads like a failed part.
Fix Step-by-step
- Run the two-light check first: ignition on, your receiver behind the headunit lights solid red. Ignition and parkers on, your wheel buttons backlight. Dark buttons mean no power at your wheel.
- Switch your lights on and off while you press a button: controls that come and go with your lights is the booster's symptom, and it rules out button mapping.
- Check your horn is wired straight to the pad: the horn wire from your clock spring goes direct to the back of your horn pad, and your wireless module piggybacks off that same crimp. Common mistake: running your horn through the module instead.
- Run the booster cable: from behind your headunit receiver module to the horn 12 volt pin at the bottom of your clock spring, in the steering column. That's the pin your horn and your controls both feed from.
- Retest with your lights on: buttons and horn, parkers and headlights, before you put your trim back.
Notes
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Where the booster cable runs, and which one you need
The booster is a white cable, labelled horn booster, and it isn't the steering wheel control connector. Those are two different plugs, and mixing them up is the first wrong turn.
- Power from: the wiring harness behind the wireless module receiver cable, which connects behind your headunit.
- To: the horn pin at the bottom of your clock spring, on the steering column side. The cable feeds that pin and boosts it.
Count the pins before you order a replacement. A 12 pin booster comes with all of our kits and suits most vehicles. The facelift 200 Series LandCruiser uses a 14 pin booster instead, so that's the one to ask for if yours is a facelift 200.
Your existing horn wiring stays exactly as it is.
Horn booster install video
See where the booster cable connects, and how your original horn wire goes to the back of your horn pad.
When it isn't the booster
Your horn, your stability control, your airbag light and your wheel buttons all stopping at once is one part, not four. Those run through your clock spring, and it gets damaged during a wheel change. Your buttons go with it because the transmitter takes its power from the horn circuit.
Get your clock spring replaced first, then retest. If your horn comes back and your buttons stay dead with your lights off, the module set is the next thing to look at rather than the supply.