Brake lights?....Really sensitive/flashing?
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Elder User
Joined: Sep 2005
Posts: 837
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From: Standish ME
Brake lights?....Really sensitive/flashing?
Hey all...I have been having problems with my brake lights being really sensitive. Like when i put pressure on the pedal and then release a tiny bit of pressure the lights shut off and then back on with barely any movement of my foot. I know this happens when you first start to brake and you are barely putting any pressure on the pedal, but this is happening to me after the pedal is most of the way down or all the way down. My cruise also doesn't work. I know the cruise is linked to the brake lights but what would be making my lights so sensitive to pedal pressure? is there a brake sensor that might need to be replaced? Thanks
FOREIGN GURU
Joined: Jul 2006
Posts: 7,655
Likes: 7
From: Celaya, Gto. MX
Hey all...I have been having problems with my brake lights being really sensitive. Like when i put pressure on the pedal and then release a tiny bit of pressure the lights shut off and then back on with barely any movement of my foot. I know this happens when you first start to brake and you are barely putting any pressure on the pedal, but this is happening to me after the pedal is most of the way down or all the way down. My cruise also doesn't work. I know the cruise is linked to the brake lights but what would be making my lights so sensitive to pedal pressure? is there a brake sensor that might need to be replaced? Thanks
Posting Guru
Joined: Nov 2007
Posts: 2,158
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From: West Texas
You need to adjust the rear brakes properly.
You also may have one of the brake boosters that leaks down too. Either one will cause it. It's not an electrical problem with the brake lights.
The cruise could be something as stupid as a fuse. Check them all first.
You also may have one of the brake boosters that leaks down too. Either one will cause it. It's not an electrical problem with the brake lights.
The cruise could be something as stupid as a fuse. Check them all first.
Post Fiend
Joined: Oct 2003
Posts: 5,903
Likes: 1
From: MICHIGAN
The sensor (BPA) on the end of the master cylinder is a redundant brake switch that deactivates the CC. The brake lights are turned on/off with a sensor (BOO) connected to the brake pedal under the dash.
The BPA has been recalled due to causing fires. You may be able to get e new one from the the dealer....free. About $25 if need to it. This may solve both of the problems.
The BPA has been recalled due to causing fires. You may be able to get e new one from the the dealer....free. About $25 if need to it. This may solve both of the problems.
Posting Guru
Joined: Nov 2007
Posts: 2,158
Likes: 0
From: West Texas
Let's not confuse him too much yet. The most common cause of this exact problem is the bad early type brake booster and misadjusted brakes. The booster isn't holding enough pressure back on the brake pedal to keep the light on.
I think the cruise is a separate problem.
Easy way to check this is to listen for air sucking. In it's final death throws you will hear that when you push the brake and hold it.
Also the pedal feels mushy and goes down a lot farther than it should.
It would be real easy to stick your head under there and with the engine running, door chime unplugged so you can hear , push the pedal down just enough to click the switch on. Does the pedal shaft go into the booster more and release the switch?
Bad booster if so. There is a Ford service bulletin explaining this exact problem.
You still need to adjust the rear brakes though. 90 % of the guys on this forum don't have them adjusted right I'd bet.
I think the cruise is a separate problem.
Easy way to check this is to listen for air sucking. In it's final death throws you will hear that when you push the brake and hold it.
Also the pedal feels mushy and goes down a lot farther than it should.
It would be real easy to stick your head under there and with the engine running, door chime unplugged so you can hear , push the pedal down just enough to click the switch on. Does the pedal shaft go into the booster more and release the switch?
Bad booster if so. There is a Ford service bulletin explaining this exact problem.
You still need to adjust the rear brakes though. 90 % of the guys on this forum don't have them adjusted right I'd bet.
Postmaster
Joined: Sep 2007
Posts: 4,195
Likes: 6
From: Medford Oregon
RRranch, I have to admit your correct on this. I looked and the switch is on the rod, a pressure thing. Good call and learning experience for me. Guess I always thought it was just a on/off switch on the brake peddle, like the IVS ... wrong. 
Tried to rep ya but need to spread it around more.
Tried to rep ya but need to spread it around more.
Fleet Mechanic
Joined: Aug 2007
Posts: 1,508
Likes: 2
From: The boonies by Dallas OR
So do a lot of the slack adjusters quit working? I've checked a few times and the rear brakes are good and tight.
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Posting Guru
Joined: Nov 2007
Posts: 2,158
Likes: 0
From: West Texas
The adjusters do suck on these trucks. I'va never worked on one yet that stayed adjusted right on it;s own.
The switch on the pedal is just a simple on off switch but if the brake booster isn't holding then the rod slacks up as tou are holding the pedal down and it's a constant on off thing on the switch. I just went through this on my 94 again. First time for me since I worked at Ford. I put a new booster on it from my 97 and problem solved. Mine was real messed up with the electric brake controller too. Since it's activated by the brake lights, it was turning on and off too when I stopped and would never hit full pressure on the trailer brakes. A little scary sometimes.
The switch on the pedal is just a simple on off switch but if the brake booster isn't holding then the rod slacks up as tou are holding the pedal down and it's a constant on off thing on the switch. I just went through this on my 94 again. First time for me since I worked at Ford. I put a new booster on it from my 97 and problem solved. Mine was real messed up with the electric brake controller too. Since it's activated by the brake lights, it was turning on and off too when I stopped and would never hit full pressure on the trailer brakes. A little scary sometimes.
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