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Discussion Starter · #1 ·
Ok. Parked the truck. Went into a store. came back out. Started the engine.
Released the brake and the brake light on the dash did not go off.
Checked the brake fluid. Was full.
Checked to see if the brake released or not. It released.
Anyone have any idea what the most common cause of that would be?
Considered the brake peddle not lifting all the way. It feels like it is all the way up.
Wire harness at the master cylinder look good. Were replaced along with the master cylinder not to long ago, Previous owner fix.
Truck does not pull one way or the other and hubs not getting hot so I presume the brakes are not stuck.

Haven't had the time to check the switch at the peddle to see if it is busted. Assuming it is at the peddle.
Oh, almost forgot. The ABS light is on most of the time. Would that effect the brake light on the dash?
Thanks.
 

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the switch at the pedal is the likely culprit

the abs light has no impact ,, that's going to be a faulty ABS sender
 

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Discussion Starter · #3 ·
Thanks. Will reach up in there and see what I find. Wiggle a few wires etc and see if that makes a difference. :poke:

Do you know if the switch is closed when the peddle is up (brakes engaged) or down (disengaged)?
 

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Low vacuum can also cause the dash brake light to illuminate (as well as the aforementioned parking brake and low fluid). Parking brake switch will close with the parking brake engaged. Cheers!
 

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Discussion Starter · #5 ·
Most switches brake and will not close. Thus the light should not come on if the switch is busted...maybe.
So, Moving on to the next mentioned possibility.....
Assuming I have low vacuum pressure. What other symptoms should I look for that may indicate a low vacuum pressure?

Thanks.
 

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A simple check for the parking brake signal switch would be to unplug the single wire going to the switch. That wire is "looking" for a ground to illuminate the light on the dash. That will rule out that problem
 

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Discussion Starter · #7 ·
Thanks, will definetly give that a try.
 

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had this happen to me once, i blew the fuse for the brake lights... check to see when you press the peddle if the lights even come on. but i think it was flashing at me, not sure
 

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Discussion Starter · #9 ·
Worth a look. But knowing my luck, it won't be that easy.

Thanks. Crossin my fingers that is it. Will check it in the AM.
 

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Discussion Starter · #10 ·
Brake lights working just fine. So, that aint it.
Will be checking the switch when I get some time, Probably this weekend.

Anyone have any ideas what symptoms would occur with low or no vacuum?
Just so I can compare to what it is doing now. Crossin my finners that it aint the vacuum system.
 

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Anyone have any ideas what symptoms would occur with low or no vacuum?
Just so I can compare to what it is doing now. Crossin my finners that it aint the vacuum system.
Hard pedal, HVAC control malfunctions, poss. noise (chirp, squeak, hiss) from the vacuum pump.
 

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Discussion Starter · #12 ·
Thanks. None of those symptoms exist so...must be the switch or wiring.
Much releaved. :woot:
 

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With low vacuum, the brakes generally get very stiff. If you put your thumb on the end of the hose off the vacuum pump, it should suck on it pretty hard at idle. Cheers!
 

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Discussion Starter · #14 ·
Thanks everyone. The shop called and they have an opening for Friday. Gonna get a few things fixed. Fuel leak and block warmer first. Since he got an opening before I could check on the switch and wiring, I think I will just add that to his list.
This mechanic is worth waiting for. He is good and inexpensive. Doesn't fix things that don't need fixin.
 

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let me know. ive got about the same issue. basically when my truck is parked ill start it up, disengage the parking brake. light stays on. about 10 seconds later it will go out. i think its a vac. issue. havnt had time to start looking into it yet
 

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Discussion Starter · #16 ·
Mine definetly is not the same symptoms as yours. Mine stays on period, won't go off at all. Brakes work just fine. Definetly not lack of vac there.
I will let you know what he finds out about it.
Yours may be a leaking vac line so check all your rubber and hard plastic lines for deterioration. If they look bad or the black from the rubber ones rubs off on your hands...replace the line.
I probably should do that on mine, rubber lines and hoses only lasts about 10 to 15 years on any vehicle. Went through that on my old 89 suburban (gasser). Had to replace just about Every vac line it had. I just know on more modern vehicles, the vac system can be complex and me not knowing how the vac system on a diesel lays out........:scared:
 

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Vacuum on these trucks is very simple. There is no "vacuum system on a diesel". A diesel engine produces no vacuum. To deal with this, Ford could have used hydroboost (hydraulic fluid from the power steering pump) for power brakes, and simple electrical or cable-based mechanical HVAC controls. But given Ford's predilection for hanging onto archaic technology, they added a separate vacuum _pump_, just so they could keep the old-school vacuum brake boost AND HVAC controls. So all we have is a pump, a distribution box, the brake booster and the HVAC box. Oh, and there's a sensor on the distribution box; if it senses inadequate vacuum, it turns on the BRAKE(!) light, which means you still have solid brakes, but it'll take monster pedal effort to use them.
 

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Discussion Starter · #18 ·
Wow, archaic is right. At least it is fairly simple. To bad it aint so simple or cheep to replace it all with something better.

Thanks. I'm learning something every day.
 

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Discussion Starter · #20 ·
The truck is due to go in this morning to the shop.
Won't know anything till this afternoon or evening.:please:..I hope it is at least that early and not like...Monday. Got a few minor things I want to do to the truck.
Things I can do my self. :D Or at least give it a good try.

I will let yall know what he comes up with about that brake light on the dash for sure.
 
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