How to Install a Hydraulic Brake Pressure Switch

Installing a pressure switch for a rear brake on a motorcycle is a relatively straightforward process, especially if you're replacing a mechanical brake light switch with a hydraulic one. Hydraulic pressure switches are also commonly known as a "Hydrostop".

Here's a step-by-step guide on how to install it:

Tools and Materials Needed:
- Hydraulic brake pressure switch (make sure it's compatible with your motorcycle)
- Wrench set (appropriate size for the banjo bolt on your brake line)
- Brake fluid (matching your motorcycle's spec, typically DOT 3, 4, or 5)
- Electrical connectors (if necessary)
- Wire strippers and crimpers
- Zip ties or electrical tape
- Brake bleeding kit

Steps:

1. Preparation:
- Park the motorcycle on a stable surface, preferably using a motorcycle stand to keep it upright.
- Turn off the motorcycle, and ensure the brake system has cooled down if the bike was recently used.

2. Locate the Rear Brake Master Cylinder:
- Find the rear brake master cylinder and the brake line connected to it. This is where you will install the hydraulic pressure switch.
- The switch typically replaces the **banjo bolt** that connects the brake line to the master cylinder or caliper.

3. Remove the Banjo Bolt:
- Use the appropriate wrench to remove the banjo bolt that attaches the brake line to the master cylinder or rear caliper.
- Be ready for a small amount of brake fluid to leak when you remove the bolt. Have a rag handy to catch the fluid.

4. Install the Pressure Switch:
- Take the hydraulic pressure switch and replace the banjo bolt with the pressure switch. The switch kit comes with a new banjo bolt and washers (usually two copper crush washers, one above and one below the brake line fitting).
- Tighten the pressure switch bolt to the torque specifications outlined in your motorcycle's service manual.

5. Connect the Wiring:
Some kits, like the Bonamici Racing kits, will have a plug-and-play connection to the OEM wiring.  If your kit does not include this no-cut harness, simply follow the following steps:
- The pressure switch will have two wires coming out of it. These wires need to be connected to the existing brake light circuit.
- Locate the wires for the rear brake light switch (usually near the brake pedal or in the wiring harness running along the frame).
- Disconnect the old switch or tap into these wires using crimp connectors or other suitable connections.
- Connect the two wires from the pressure switch to the brake light circuit. It doesn’t matter which way you connect them, as the switch simply completes the circuit when the brake is pressed.

6. Bleed the Brake System:
- Since you've opened up the brake line, air has been introduced into the system. You'll need to bleed the rear brake to remove air bubbles and restore full braking function.
- Follow the brake bleeding procedure outlined in your motorcycle's manual. Typically, this involves topping off the brake fluid, pumping the brake pedal, and releasing air from the brake caliper bleeder valve until only brake fluid flows out.

7. Test the Switch:
- After everything is connected and the brake system is bled, turn on the ignition (but don’t start the bike).
- Press the rear brake pedal. The brake light should activate as soon as pressure is applied to the brake line.
- Check for any leaks around the new pressure switch.

8. Secure Wiring:
- Use zip ties or electrical tape to neatly secure the wiring for the pressure switch to the frame or existing wiring harness. Ensure that the wires do not interfere with any moving parts or get pinched.

Final Checks:
- Double-check all connections and make sure everything is secure.
- Take the motorcycle for a short test ride, and ensure the rear brake light activates when the brake pedal is pressed.

By following these steps, you should be able to successfully install a hydraulic pressure switch for your rear brake.