Brake light diag
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Laughing Gas
Joined: Jul 2001
Posts: 849
Likes: 14
From: Fayetteville, NC
Brake light diag
The brake light on the dash is on a 1989 F150 and stays lit while parking brake is off, but only dimly. Could it be the parking brake release switch is just bad or would something else trigger the light to stay dimly lit?
Mountain Pass
Joined: Aug 2023
Posts: 150
Likes: 97
From: Alabama
Assuming your fluid level is good, have you worked on the brakes lately?
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Laughing Gas
Joined: Jul 2001
Posts: 849
Likes: 14
From: Fayetteville, NC
No. The brakes haven't been touched in a while. Like you, the ABS light is on as well (I pulled that and cleaned it, but it made no difference) but that's separate from the brake light. I checked the fluid level and made sure the float in the master cylinder still floats. I can set the parking brake and the light comes on bright and if I push on the button it only goes dim and not out completely.
Hotshot
Joined: Jun 2015
Posts: 12,791
Likes: 2,426
The master cylinder will also turn on the red brake light.
The red brake light will cause the ABS light to turn on. There is no valve that needs to be centered. It isn’t a proportioning valve.
That does not mean that the sensor on the master cylinder isn’t triggering the light.
The red brake light will cause the ABS light to turn on. There is no valve that needs to be centered. It isn’t a proportioning valve.
That does not mean that the sensor on the master cylinder isn’t triggering the light.
Mountain Pass
Joined: Aug 2023
Posts: 150
Likes: 97
From: Alabama
The master cylinder will also turn on the red brake light.
The red brake light will cause the ABS light to turn on. There is no valve that needs to be centered. It isn’t a proportioning valve.
That does not mean that the sensor on the master cylinder isn’t triggering the light.
The red brake light will cause the ABS light to turn on. There is no valve that needs to be centered. It isn’t a proportioning valve.
That does not mean that the sensor on the master cylinder isn’t triggering the light.
Good to know - thanks!
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Laughing Gas
Joined: Jul 2001
Posts: 849
Likes: 14
From: Fayetteville, NC
So I bought a new master cylinder and plugged it in and flipped it upside down so the float is at the top. Turned the key on and the brake light and ABS lights are still on. That tells me the master cylinder isn't the culprit. Are there grounds associated with the system that can be checked?
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Laughing Gas
Joined: Jul 2001
Posts: 849
Likes: 14
From: Fayetteville, NC
Bled the brakes tonight and that didn't do a thing. Is there a way to test the abs module that's next to the gas pedal?
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