Intermittent brake warning light - Ford Powerstroke Diesel Forum
 
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post #1 of 6 Old 05-23-2017, 05:38 AM Thread Starter
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Intermittent brake warning light

I have an intermittent brake warning light issue for a few months now. Disconnected the emergency brake switch and tested; switch is good and light still comes on with it disconnected. I should add the light is very random and sometimes fades on and off. I replaced the brake master cylinder because it's 20 years old, still comes on. The worst of it is, it disables the cruise control when on. Harness?

97 F350 XL std cab, zf5, srw (converted), 4wd, 3.55s, stock wheels/tires & rebuilt 9.18
2 Donaldsons, 3" dp, ACs, T500, HV LPOP, Hydra w/PHP, DIY 60 gl tank w/6 gl sump, eFuel/Cat filters, Aeromotive RR, Auber instruments, 140v IDM, KC 300X 63/70/84, boost fooler, RiffRaff bellowed up pipes, 6.0 IC, 3" plenums w/RiffRaff inserts & SB 425HD
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post #2 of 6 Old 05-23-2017, 05:40 AM
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I have an intermittent brake warning light issue for a few months now. Disconnected the emergency brake switch and tested; switch is good and light still comes on with it disconnected. I should add the light is very random and sometimes fades on and off. I replaced the brake master cylinder because it's 20 years old, still comes on. The worst of it is, it disables the cruise control when on. Harness?
Check the ground

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post #3 of 6 Old 05-23-2017, 05:43 AM Thread Starter
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Ah, which one? Grounding is how the system powers the brake problem light.

97 F350 XL std cab, zf5, srw (converted), 4wd, 3.55s, stock wheels/tires & rebuilt 9.18
2 Donaldsons, 3" dp, ACs, T500, HV LPOP, Hydra w/PHP, DIY 60 gl tank w/6 gl sump, eFuel/Cat filters, Aeromotive RR, Auber instruments, 140v IDM, KC 300X 63/70/84, boost fooler, RiffRaff bellowed up pipes, 6.0 IC, 3" plenums w/RiffRaff inserts & SB 425HD
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post #4 of 6 Old 05-23-2017, 05:47 AM Thread Starter
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I tested the switches on the NEW master cylinder too; light is still coming on. I have heard of the float sticking, I was hoping it was that. That is the main reason I replaced the original master cylinder

What about the vacuum pump or switch?

97 F350 XL std cab, zf5, srw (converted), 4wd, 3.55s, stock wheels/tires & rebuilt 9.18
2 Donaldsons, 3" dp, ACs, T500, HV LPOP, Hydra w/PHP, DIY 60 gl tank w/6 gl sump, eFuel/Cat filters, Aeromotive RR, Auber instruments, 140v IDM, KC 300X 63/70/84, boost fooler, RiffRaff bellowed up pipes, 6.0 IC, 3" plenums w/RiffRaff inserts & SB 425HD

Last edited by MeTo; 05-23-2017 at 06:10 AM.
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post #5 of 6 Old 05-23-2017, 09:43 PM
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Doesnt the prop valve have a wire going to it? Might be confusing it with my other truck
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post #6 of 6 Old 05-24-2017, 08:06 AM Thread Starter
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The low vacuum switch is bad. I checked the system with my old vacuum gauge and it's showing ~23 inches plus gauge error. I also checked about 45 minutes later and it still had ~23 inches. I would think the switch is a discontinued item? Has anyone found a replacement or repaired the original switch?

97 F350 XL std cab, zf5, srw (converted), 4wd, 3.55s, stock wheels/tires & rebuilt 9.18
2 Donaldsons, 3" dp, ACs, T500, HV LPOP, Hydra w/PHP, DIY 60 gl tank w/6 gl sump, eFuel/Cat filters, Aeromotive RR, Auber instruments, 140v IDM, KC 300X 63/70/84, boost fooler, RiffRaff bellowed up pipes, 6.0 IC, 3" plenums w/RiffRaff inserts & SB 425HD
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