Haltech Nexus Brake Pedal Switch Setup in NSP: Wiring & Input Settings

A brake pedal switch is one of the cheapest inputs you can give a Nexus ECU, and one of the most useful. It adds a safety check for drive-by-wire, cancels cruise control and can lock out the starter. Here's how we wire it and set it up in NSP.

What the ECU uses it for

Knowing when the brake is pressed lets the ECU do a surprising amount: extra safety logic for drive-by-wire throttles, cancelling cruise control, a starter lockout that requires the brake before cranking, and plenty of custom conditions and logging. The Nexus supports two brake switch inputs, which is handy when you want a second switch for redundancy.

Choosing the input mode

Brake Pedal Switch 1 Input Mode: choose Digital - Switched if the switch is wired to the ECU, or CAN Input if the vehicle's CAN bus already broadcasts brake status to the ECU.
Brake Pedal Switch 2 Input Mode: Digital - Switched for a second, hard-wired switch, or Disabled if you only have one.

Wiring and connection settings

Most brake switches are wired between an ECU input and ground. When you press the pedal (for a normally open switch), the switch closes and pulls the input down to ground. The ECU needs a pull-up to hold the input high the rest of the time. You can use either an analog input or a digital (SPI) input:

Input type	Settings for a normally open switch	For a normally closed switch
Analog input	On Voltage 2.0V, Off Voltage 3.0V, Pull Up enabled. The input sits at 5V and drops to ground when the switch closes	Swap the On and Off voltages
Digital (SPI) input	Edge Select Falling, Sensor Type Hall Effect, Pull Up enabled. The input sits at 12V and drops to ground when the switch closes	Set Edge Select to Rising

The gap between the on and off voltages on an analog input acts as hysteresis. It keeps a slightly noisy signal from flickering between pressed and released.

Tip

Many cars have a brake switch with two circuits: one for the brake lights (usually switching +12V) and a separate one meant for the factory ECU or cruise control. Use the ECU circuit if there is one. If you tap the brake light circuit instead, you'll be feeding 12V into the input, so the ground-switching settings above won't apply as written. Ask us if you're not sure which circuit you have.

Check it works

With the ignition on, watch the brake pedal switch channel in NSP and press the pedal a few times. It should change state every time, with no lag or flicker. If it shows pressed with your foot off the pedal, the switch is the opposite type to what you've configured; swap the voltages or the edge.

FAQ

Do I need a brake switch for drive-by-wire?

It adds another safety check to the throttle logic by telling the ECU when the driver is braking, so we recommend one on any drive-by-wire build.

Is this different on an Elite ECU?

The concept is the same, but the software screens differ. See our Elite brake pedal switch article.