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Discussion Starter #1
I have searched this and other forums to try to solve this problem, but still have not found an answer to my issue. We have 1997 F-250HD. The Brake light illuminates at various times, and when it comes on during driving with the cruise control, the cruise will shut off. Occassionally the Brake light will be dim, or even flicker, at other times it come on bright and steady. I know there are only 3 main sources tied to this light:
emergency brake
low vacuum
low brake fluid

We have put in two different vacuum pumps, and have good vacuum from the pump. Brake fluid is full and does not drop down significantly when brakes are applied. Ebrake switch works and does not seem to be the problem.

Here is what we know:
1. At idle with transmission in neutral, pumping the brakes 1-3 times will stiffen the brake pedal and the Brake light will illuminate. Takes 10 seconds to couple minutes to go off.
2. If we unhook the low vacuum switch and the vacuum distribution manifold, the brake light does not come on with the above brake pump test, and I think does not come on during driving conditions (need to run more to make sure).
3. We unhooked the low brake fluid switch from the master cylinder for a while and seemed to fix the Brake light/cruise issue, but did not test this very long.
4. This issue "seems" to be worse in cold or damp conditions.

I have read the Brake light/cruise control issue must be tied to the low brake fluid source because that is what links these two. If that is the case I cannot figure out why, when the low vacuum switch is unplugged, the Brake light does not illuminate.

Admittedly we have not tested everything, and some of the above may be conflicting. I am not an expert on this obviously, so would like to get anyone's thoughts on what could be going on here and how to test. I am pretty certain of two things: this is not an issue with the emergency brake switch, and the vacuum pump is good.

Thank you to each and all who may have some ideas on this. CBS
 

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I can't explain why the light wouldn't come on with the vacuum disconnected??? Anyway, maybe check out the switch on the end of the master cylinder AND if you haven't had the recall performed on it for that switch have that done too (I chose to just buy the part (Ford SW6350) and install it myself rather than take it to the dealer that's 60 miles away):

SPEED CONTROL SYSTEM MODIFICATION
NHTSA Recall Number:
09V399000 NHTSA Date: OCT 13, 2009 Ford Recall number: 09S09
Recall Description:SPEED CONTROL SYSTEM MODIFICATION

Risk to Safety:A VEHICLE FIRE COULD OCCUR WITH OR WITHOUT THE ENGINE RUNNING.

Remedy Program: FORD WILL NOTIFY OWNERS THAT DEALERS WILL INSTALL A FUSED WIRING HARNESS IN LINE WITH THE SCDS. ON 1999-2003 WINDSTAR VEHICLES WITH A LEAKING SCDS, DEALERS WILL ALSO INSPECT THE ABS CONTROL MODULE CONNECTOR AND REPAIR AS NECESSARY. REPAIRS WILL BE COMPLETED FREE OF CHARGE. THE SAFETY RECALL BEGAN ON OCTOBER 27, 2009. OWNERS MAY CONTACT FORD AT 1-888-222-2751.

Manufacturer Notes:TO CHECK FOR NON-SAFETY-RELATED PROGRAMS APPLICABLE TO YOUR VEHICLE, SEE HTTP://WWW.FORD.COM/ OR WWW.LINCOLN.COM OR CALL YOUR FORD OR LINCOLN DEALER.

Cheers!
 

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Discussion Starter #3
I can't explain why the light wouldn't come on with the vacuum disconnected??? Anyway, maybe check out the switch on the end of the master cylinder AND if you haven't had the recall performed on it for that switch have that done too (I chose to just buy the part (Ford SW6350) and install it myself rather than take it to the dealer that's 60 miles away):

SPEED CONTROL SYSTEM MODIFICATION
NHTSA Recall Number:
09V399000 NHTSA Date: OCT 13, 2009 Ford Recall number: 09S09
Recall Description:SPEED CONTROL SYSTEM MODIFICATION

Risk to Safety:A VEHICLE FIRE COULD OCCUR WITH OR WITHOUT THE ENGINE RUNNING.

Remedy Program: FORD WILL NOTIFY OWNERS THAT DEALERS WILL INSTALL A FUSED WIRING HARNESS IN LINE WITH THE SCDS. ON 1999-2003 WINDSTAR VEHICLES WITH A LEAKING SCDS, DEALERS WILL ALSO INSPECT THE ABS CONTROL MODULE CONNECTOR AND REPAIR AS NECESSARY. REPAIRS WILL BE COMPLETED FREE OF CHARGE. THE SAFETY RECALL BEGAN ON OCTOBER 27, 2009. OWNERS MAY CONTACT FORD AT 1-888-222-2751.

Manufacturer Notes:TO CHECK FOR NON-SAFETY-RELATED PROGRAMS APPLICABLE TO YOUR VEHICLE, SEE HTTP://WWW.FORD.COM/ OR WWW.LINCOLN.COM OR CALL YOUR FORD OR LINCOLN DEALER.

Cheers!
Thanks for the comments. Clarification, the light does not come on when the vacuum "switch" or sensor that plugs into the end of the vacuum distributor manifold is unhooked. Not the vacuum hose.

We have replaced that recall switch on the master cylinder. Same as you I just bought one rather than the recall. I guess the new one could be bad.

Thanks again for the comments/thoughts. Keep them coming if you can think of anyhting else.

CBS
 

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Check the brake switch on the pedal? Mine went bad and the brake lights would take 10-15 seconds to turn off.


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The Low Vacuum Warning Switch (solid state) is normally open. It closes to illuminate the Brake Warning light when the vacuum stays below 10 inches for more than 7 seconds. So, if you disconnect the switch the light shouldn't come on due to that, but if you disconnect the hose, the hose the light should come on (engine running). Attached is the diagram for the Brake Warning Light from the EVTM if you need it. Cheers!
 

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Occassionally the Brake light will be dim, or even flicker, at other times it come on bright and steady.
That's a classic symptom of a chafed wire being intermittently shorted to ground, with some resistance. Look for anything under the hood or dash that could pinch the wiring harness.
I know there are only 3 main sources tied to this light: emergency brake, low vacuum, low brake fluid
The circuit is more complex than that...

D & E come from the same circuit: fuse 17 R/Y (hot in START or RUN).

The ignition switch is also an input to the BRAKE warning indicator, for the prove-out during cranking, which also triggers the RABS to prove-out its warning indicator. Note that a fault in the DRL (or its jumper) can also result in the BRAKE warning.

202434


Ebrake switch works and does not seem to be the problem.
Have you tried driving with that wire unplugged?
I have read the Brake light/cruise control issue must be tied to the low brake fluid source because that is what links these two.
That's a large jump to a conclusion, without any diagnosis or logic.
...I cannot figure out why, when the low vacuum switch is unplugged, the Brake light does not illuminate.
Because it's a normally-open circuit, and unplugging it makes it semi-permanently open. So the circuit behaves as if there's good vacuum.
 

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Discussion Starter #7
All the replies are much appreciated. Seems I have several more possibilities to look in to:
1. I think I unplugged and ran without the emergency brake switch hooked up, but can't remember. I will do that again.
2. Agree, it does sound like an occasional short/grounding issue somewhere. In my mind I was hoping to avoid electrical issues, which I am less comfortable testing (or in many cases don't know how to test). Chasing down chaffed wires does not sound pleasant to me.
3. Other parts of the circuit - I will review your comments and the EVTM to see where those may lead. I'm going to need to read the EVTM instructions so I know how to read the diagrams, symbols, etc. If I can figure out how to diagnose these I think I may start there. Cheaper than semi-educated guesses leading to replacing parts.


Again, I appreciate very much the comments/guidance.

CBS
 

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To find a chafed or pinched wire that's intermittently shorting to ground, connect a digital multimeter (DMM) from anywhere on the suspect circuit (either DG/Y or Pu/W) to any reliable ground (battery negative, green ground bolt, engine, brake line at the MC...) and set it to diode test (so it makes a noise when the probes touch each other). Then gently wiggle the wiring harness sections that contain the suspect circuit, while listening for the DMM sound. Ford calls it a "wiggle test", and it's described in the EVTM.
 

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Following, because I have the EXACT same issue. Tends to happen most often when the vehicle is cold and ambient temps are low(ish). I have not gotten around to troubleshooting it yet, but it is on my list of things to do. The cruise cutting out is obnoxiously annoying.
 

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Discussion Starter #10
Following, because I have the EXACT same issue. Tends to happen most often when the vehicle is cold and ambient temps are low(ish). I have not gotten around to troubleshooting it yet, but it is on my list of things to do. The cruise cutting out is obnoxiously annoying.
Good luck. Some good advice from guys on here. Let's figure this out together!!
 
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To find a chafed or pinched wire that's intermittently shorting to ground, connect a digital multimeter (DMM) from anywhere on the suspect circuit (either DG/Y or Pu/W) to any reliable ground (battery negative, green ground bolt, engine, brake line at the MC...) and set it to diode test (so it makes a noise when the probes touch each other). Then gently wiggle the wiring harness sections that contain the suspect circuit, while listening for the DMM sound. Ford calls it a "wiggle test", and it's described in the EVTM.
Thoughts on whether a bad brake controller could cause feedback to the brake line? My brake controller (cheapo, probably 10 years old) works when trailer is hooked up, but generally acts like it does not work when trailer is not hooked up. Just an thought, and I saw that mentioned on another conversation.
 

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Normally a brake controller won't do anything when a trailer is not hooked up. The LED on mine is lit when a trailer with brakes is hooked up and dead without. If you thought it might be a problem, disconnect it and see if the problem shows up. Is yours wired to the factory harness connection under the dash? Cheers!
 

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Thoughts on whether a bad brake controller could cause feedback to the brake line? My brake controller (cheapo, probably 10 years old) works when trailer is hooked up, but generally acts like it does not work when trailer is not hooked up. Just an thought, and I saw that mentioned on another conversation.
Check your wiring at the trailer plug. Seen many with corrosion that will cause it to back feed.

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Normally a brake controller won't do anything when a trailer is not hooked up. The LED on mine is lit when a trailer with brakes is hooked up and dead without. If you thought it might be a problem, disconnect it and see if the problem shows up. Is yours wired to the factory harness connection under the dash? Cheers!
Nope, for some reason prior owner decided to bypass the factory tow package wiring harness. I will unhook it and see what happens. Thanks
 

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I have searched this and other forums to try to solve this problem, but still have not found an answer to my issue. We have 1997 F-250HD. The Brake light illuminates at various times, and when it comes on during driving with the cruise control, the cruise will shut off. Occassionally the Brake light will be dim, or even flicker, at other times it come on bright and steady. I know there are only 3 main sources tied to this light:
emergency brake
low vacuum
low brake fluid

We have put in two different vacuum pumps, and have good vacuum from the pump. Brake fluid is full and does not drop down significantly when brakes are applied. Ebrake switch works and does not seem to be the problem.

Here is what we know:
1. At idle with transmission in neutral, pumping the brakes 1-3 times will stiffen the brake pedal and the Brake light will illuminate. Takes 10 seconds to couple minutes to go off.
2. If we unhook the low vacuum switch and the vacuum distribution manifold, the brake light does not come on with the above brake pump test, and I think does not come on during driving conditions (need to run more to make sure).
3. We unhooked the low brake fluid switch from the master cylinder for a while and seemed to fix the Brake light/cruise issue, but did not test this very long.
4. This issue "seems" to be worse in cold or damp conditions.

I have read the Brake light/cruise control issue must be tied to the low brake fluid source because that is what links these two. If that is the case I cannot figure out why, when the low vacuum switch is unplugged, the Brake light does not illuminate.

Admittedly we have not tested everything, and some of the above may be conflicting. I am not an expert on this obviously, so would like to get anyone's thoughts on what could be going on here and how to test. I am pretty certain of two things: this is not an issue with the emergency brake switch, and the vacuum pump is good.

Thank you to each and all who may have some ideas on this. CBS
there is a brake light switch at the base of the brake pedel inside the cab
Disconnect it and see if the problem goes away
 

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Nope, for some reason prior owner decided to bypass the factory tow package wiring harness.
You should add all those details to your signature, and then try to restore as much of the wiring to factory configuration as possible. You can re-install the electrical modifications later, if you choose to. We'll help you put them in the right way after this problem is solved.
there is a brake light switch at the base of the brake pedel inside the cab
Disconnect it and see if the problem goes away
Don't attempt to drive vehicle with an electronically-controlled transmission (like the E4OD) with the BOO disconnected. The transmission won't behave correctly, and there could be other problems. If the truck has a shift interlock, it will be difficult to get the shifter out of Park when the BOO is unplugged.

(phone app link)
 
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