Brake Light Switch Diagnosis and Replacement

Bulb fine but no brake light? It is usually the switch — and there are two of them.

A brake light that does not come on is not usually a bulb. Bulbs tend to fail for the tail and brake filament at different times, so the usual symptom is: tail light works, brake light does not. That points at a switch or its wiring, and knowing there are TWO switches saves most of the diagnostic time.

Tools

• Multimeter or test light
• Basic hand tools
• Service manual with the wiring diagram
• Brake fluid and bleed kit — only if yours is a hydraulic pressure switch

Diagnose before you buy anything

First establish what actually works. With the ignition on: does the tail light glow? Does the brake light come on with the FRONT lever? With the REAR pedal? Test each independently — most people only ever test one.

If the front lever lights it and the rear pedal does not, the bulb and the circuit to the lamp are fine. The fault is the rear switch or its wiring. The reverse is equally informative.

If neither lights it and the tail light works, suspect the brake filament, the common feed, or a fuse shared by both switches.

Check the fuse before anything else. It is free and it is sometimes the answer.

A mechanical switch can be tested with a multimeter for continuity as it is operated. A hydraulic pressure switch closes on brake line pressure — squeezing the lever with the wheel free should close it.

Rear brake switch

On models with a mechanical rear switch, it is operated by the brake pedal linkage and is usually adjustable. A rear brake light that comes on late, or stays on, is often just out of adjustment rather than faulty — check adjustment before replacing.

A rear light that stays on permanently will flatten the battery and, worse, removes your ability to warn traffic. Treat it as urgent, not cosmetic.

On models with a hydraulic pressure switch, the switch is part of the brake hydraulic circuit. Removing it opens the system, which means the brakes must be bled properly afterwards. If you are not confident bleeding brakes, this is the point to stop and hand it over.

Front brake switch

The front switch sits in the hand control housing at the lever. Access usually means opening the switch housing, which on many models also contains the other handlebar switches and their wiring.

Work slowly and photograph the routing before you disturb anything. Handlebar switch housings are full of thin wires in tight loops and it is easy to trap one when the halves go back together.

Check the wiring where it enters the bars before condemning the switch. Wires that flex with the steering fail at the flex point, and an intermittent brake light is far more often a broken strand than a bad switch.

After the repair

Test both switches again, separately, with the engine off and ignition on.

Have someone stand behind the bike, or use a reflective surface, and confirm the light is noticeably brighter on the brake than on the tail. A brake light that is on but not brighter is a bulb fitted the wrong way round in a dual-filament holder, or a failed filament.

If you opened a hydraulic circuit, bleed the brakes and check for a firm lever before the bike moves.

Parts for this job

Check fitment for your own model and year before ordering — add your bike and we will flag what fits.

Other Harley how-to guides

This guide covers procedure and judgement. Torque figures, fluid capacities, gaps and tension settings are specific to your model and year and must come from the factory service manual for your motorcycle — we deliberately do not print numbers we cannot stand behind for your bike. Independent aftermarket retailer, not affiliated with Harley-Davidson, Inc.