brake light.
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Junior User
Joined: Sep 2010
Posts: 50
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brake light.
ever sense i bought my truck the red BRAKE light is always on even when the brake isn't on. i put a new booster and master cylinder on and its still on. i thought maybe a fuse. does anyone know?
Moderator
Joined: Nov 2007
Posts: 22,415
Likes: 92
From: Denver Metro Area, CO
This has been covered quite a bit recently and there's some decent info in the archives.
Search -> Advanced Search -> search on "brake light" (WITH the quotes) and select just
in this forum, you'll find a lot of stuff to take a look at....
Search -> Advanced Search -> search on "brake light" (WITH the quotes) and select just
in this forum, you'll find a lot of stuff to take a look at....
Moderator
Joined: Jan 2001
Posts: 56,948
Likes: 2,717
From: Virginia
Take your foot, and push up on the parking brake pedal. If that doesn't make it go out, go under the hood and find the brake master cylinder. Follow the brake lines down and you should end up at a block with lots of lines and a single wire. Unplug this single wire and see if the light goes out.
pedant
Joined: Jan 2008
Posts: 23,576
Likes: 38
From: EXTREME southwest CT
I'm not certain if the setup is the same on an '80-'86, but on my 1987 the three wire plug on the side of the master cylinder reservoir was shorting internally.
When I changed my master cylinder I guess the act of forcing the plug back on finally caused a break, causing the low fluid idiot light to remain on.
Something to check, I suppose...
When I changed my master cylinder I guess the act of forcing the plug back on finally caused a break, causing the low fluid idiot light to remain on.
Something to check, I suppose...
Moderator
Joined: Nov 2007
Posts: 22,415
Likes: 92
From: Denver Metro Area, CO
That feature is available only on modern vehicles, no such capability here.But, we at least have hydraulic brakes, unlike some of our predecessors:
BTW to the OP I believe there are *two* wires but in a single connector that
Franklin2 is referring to, not just one.
Both wires are white/purple stripe, and this is the connector that needs to be
disconnected/reconnected to perform this test.
Senior User
Joined: Jun 2007
Posts: 140
Likes: 0
From: Milwaukee, WI
Assuming you are referring to the BRAKE light on the dash always being on, I would also check to make sure that your parking brake pedal is all the way up. The switch is at the end of the parking brake pedal travel.
Good Luck!
Good Luck!
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Cargo Master
Joined: Apr 2010
Posts: 2,936
Likes: 9
From: Acworth, GA
You might also check the brake switch on the proportioning valve out, as well as the valve itself. My light stayed on all the time and it turned out to be the valve that was bad.
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Post Fiend
Joined: Jul 2004
Posts: 8,786
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From: Northern California
1980-1983 did not have a switch on the parking brake pedal from the factory to activate the Brake warning lamp. First year of this is 1984.
So if we are talking about a 1980, then there is a problem with the brake system somewhere.
When you changed the master cylinder, did you bleed all the wheel cylinders and or calipers? Did you try and recenter the poroprtioning valve by firmly pressing the brakes several times after bleeding the brake system? Check for leaks in the brake system. Does the pedal remain firm when pressed firmly, or does it slowly keep going to the floor with the same amount of pressure applied?
If everything checks out, you may need a new porportioning valve, and/or porportioning valve lamp switch. Sometimes the seal on the switch get contaminated with brake fluid, or the seal fails and causes the switch on the porpotioning valve to short.
Follow these suggestions, and you should be able to figure it out.
So if we are talking about a 1980, then there is a problem with the brake system somewhere.
When you changed the master cylinder, did you bleed all the wheel cylinders and or calipers? Did you try and recenter the poroprtioning valve by firmly pressing the brakes several times after bleeding the brake system? Check for leaks in the brake system. Does the pedal remain firm when pressed firmly, or does it slowly keep going to the floor with the same amount of pressure applied?
If everything checks out, you may need a new porportioning valve, and/or porportioning valve lamp switch. Sometimes the seal on the switch get contaminated with brake fluid, or the seal fails and causes the switch on the porpotioning valve to short.
Follow these suggestions, and you should be able to figure it out.