Most likely cause is a problem with the front brake light switch located in the right switch housing on the handlebars. If you installed new levers you may have ones for a different model or the clip that holds the switch my have fallen out.
Check your brake light switches. Chances are its the front one. The clip that holds the switch in place may have fallen out or the lever isn't hitting the switch.
emergency brake light stays on
Defective or misadjusted, brake light switch.
The battery light stays on when the alternator is over or under charging. The red brake light stays on when the parking brake is set or the fluid is low. The abs light stays on when the abs computer detects a malfunction and sets a code.
brake light swith located under the brake pedal is stuck.
The brake lights work without the key on, so you have a problem with your brake light switch.
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brake light switch is broken or out of adjustment. brake light switch is located above brake pedal.
If you are referring to the brake light then the brake light switch is stuck.
With an ohmeter or a self-powered test light. Hook the two leads of your tester to the terminals on the brake light switch. Push down on the brake pedal and if the light stays off or the meter stays at infinity, the switch is bad.
check brake fluid
You will need to change the brake light switch. The brake light switch can be found below the dashboard on the drivers side.