Brake light sendind switch

D

devicemanager

Registered
I think I might need one of these. My brake lightz are very responsive, when I step on the dbrake they light up instantly. But when I pull my foot off just a hair the lights go out. This happens at whatever degree of pressure I apply. It seems like the switch doesn't come out as fast when I release pressure. Does this sound light the switch is on its wa out? Where is it located and how much of a job is it to replace?

Thanks
 
RE: Brake light sendind switch

I believe this is the way all Mark VIIIs behave. I think the switch is a "pressure" switch, so that when you slightly let up on the pressure, the brake light goes off until it senses positive pressure again. This was discussed here, (or there), before.

John
http://mark8.org/users/johnaec/Mark_VIII_s.jpg
'97 Mark VIII LSC
'96 T-Bird 4.6L
 
RE: Brake light sendind switch

The switch is mounted right behind the brake pedal right by the firewall underneath the front dashboard. if you take the black beauty cover off udner the dash you will be able to see it.
 
RE: Brake light sendind switch

Yeah, that is really annoying, and quite frankly, I consider it unsafe. Not to mention that fact that it's got to be harder on the lights, ESPECIALLY the neon light on second gens, having them cycling on and off like that. I don't know what the hell Ford was thinking when they designed it that way.

Here's something odd though: Try the brakes with the engine OFF. The brake lights work just like they should, i.e., they stay on until you take your foot completely off the pedal. You can pump it hard and it stays on throughout.

It bothers me so much I've considered looking at a switch from an older car and jury rigging something. I remember the switch on older Fords used a chain that ran from the switch on the pedal to the firewall. The switch had a simple lever that the chain attached to. Any pressure on the pedal, and the lever moved, closing the circuit. Only when the pedal was all the way back did the switch open.
 
RE: Brake light sendind switch

Well here is some news. I was still feeling like my lights weren't lighting up the way they should. So I check the brake fluid and I was a little low. Once I filled it the brake light response got much better. Check your master cyclinder fluid, you might need some like I did.
 
RE: Brake light sendind switch

This is interesting. I looked at my '93 and as far as I could tell,
the brake switch worked fine. That is to say, the brake lamps
illuminated and stayed illuminated as long as the pedal was
depressed. I could not get the switch to exhibit the release
phenomenon as discussed quite a few times here on the board.

The switch looks like this:
http://mark8.org/users/driller/pics/BOOswitch.jpg

Technically, it is known as the Brake On/Off(BOO) switch and does far
more than just switch the brake lamps. It is integrated to the PCM,
ABS, cruise control, shift interlock and multifunction switch in
addition to supplying voltage to the Rear Stop/Park/Turn Lamps and
the High Mount Stop Lamps.

But how it works is what i found intriguing. From the manual:

Stoplamp Switch, Mechanical

The mechanical stoplamp switch assembly is installed on the pin of
the brake pedal arm, so that it straddles the master cylinder push
rod. The switch assembly is a slip fit on the pedal arm pin, and the
switch pressure plate mates with the flat on the master cylinder push
rod. The switch assembly travels with the pedal arm but maintains
alignment with the flat on the push rod at all times.

The brake pedal arm pin and plastic bushing has a designed in
clearance with the eye of the master cylinder push rod. Because of
this clearance, whenever the brake pedal is pushed forward, the
stoplamp switch frame moves forward pulling the whole assembly
forward. During that movement, the push rod flat pushes the switch
pressure plate and actuating pin rearward, closing the switch
contacts. This completes the circuit to the stoplamps.

http://mark8.org/users/driller/pics/brakepedal.jpg

When the brake pedal is released, the spring in the stoplamp switch
returns the actuating pin to its normal position and the circuit to
the stoplamp opens.

One can see that it is the master cylinder push rod that activates
the switch and not the brake pedal. Having said that, it is
interesting that topping off the brake fluid in the master cylinder
reservoir improved the response of the switch. So in actuality it is
the subtle interaction between the brake pedal and the master
cylinder pushrod that is responsible for performance of the switch.
If the master cylinder pushrod maintains a back pressure against the
pivoting brake pedal, the brake lamps will stay on as long as the
pedal is depressed. But if the master cylinder pushrod hangs or
responds slower than the brake pedal, the brake lamps will go off at
the first retreat of the brake pedal.
 
RE: Brake light sendind switch

Interesting info Driller. My service manual talks about some of the same stuff the switch controls, but not how it works. I don't remember if I mentioned it, but mine seems to work properly when the engine is OFF (for at least the first few pumps), but as soon as I start her up, I get the flashing light syndrome.

There was another second gen in front of me on the way home from work yesterday, and at every stop light his brakes lights were OOOOOOOOO-----OOO-----OOOOO---OO-OOO-OO-OOOOOO. Drove me nuts looking at it. It's gotta be hell on the neon light.

I may try topping the fluid off and seeing if that makes a difference.
 
RE: Brake light sendind switch

Yeah Driller - really nice info.

Even though the fluid level is where it should be I still noticed the sensitivity of the slight release in pressure - but it is much better that it was before.
 
RE: Brake light sendind switch

Well, the problem is obviously systemic of Fords. The wife's Sable has been demonstrating symptoms of a faulty brake lamp switch. It got to the point that you had to wiggle the switch to get it to shift out of park. Alldata showed recalls to R&R the switch as well as check the adjustable pedals. The local FLM dealer took care of the pedal recall but I had to argue with them over the brake switch. Presumably the factory lube for the adjustable pedals contaminates the switch. They said 'OASIS' showed no such recall. $20 for the switch, I gave up. Why does a 48 year old 'driller' have to argue with a service tech who presumably went to school for this line of work!? Geeezzzz. I even printed out the info and faxed it to them. After a while, it's like, nevermind... just give me a new brake switch and change the oil and give her car back, I can't take this anymore! Besides, she was threatening to drive the Mark VIII!

BTW, the new switch fixed her problem, and for $20 I would change the one in my Mark if I had any trouble with the brake lights, especially if I had a Gen2 with the neon tail light.
 
RE: Brake light sendind switch

... I don't remember if I mentioned it, but mine seems to work properly when the engine is OFF (for at least the first few pumps), but as soon as I start her up, I get the flashing light syndrome.
Click to expand...

The brake pedal is linked to the vacumn booster push rod. A common test for vacumn boosters is to pump the brakes with the car off 'till a hard pedal is achieved. Hold down moderately on the brake while starting the car. You should feel the pedal resistance ease off and pedal press down a little after the engine is running.

Besides the obvious feedback resistance of the brakes, there are return springs for the vacumn booster push rod, vacumn booster diaphram, master cylinder push rod and master cylinder piston. All this mechanically linked, pneumatically assisted, hydraulically applied apparatus must work in concert consistently to maintain proper 'feel' of the brake pedal throughout its operation, from light taps to heavy application of the brakes. At the end of all this(pun intended), is the brake lamp switch.

For the BOO switch to function consistently, it must pivot freely and the spring slide action must perform without hesistation. This allows consistent alignment with the pushrod and consistent release of the contact pin after the brake pedal returns to rest. Electrically, the harness connection must be clean and provide good contact, and the switch contacts must be clean and perform consistently. How many thousands of times do you suppose the switch is cycled in its lifetime? Anyone with electrical background can relate to the problem of switch contacts.

All in all, IMHO it is NOT normal for the brake lamps to go out during ANY application of the brakes until the brake pedal is fully released. If you don't feel any difference in the pedal resistance, there should be no difference at the pushrod end. Look at the design. If the brake pedal is pushing any at all on the pushrod, the switch should be closed. If the switch is closed, the brake lamps are supposed to be on. Period. Do not fool yourself that this is a pressure actuated feedback system.

OK you say, how do you explain the improved response of switch after topping off the brake resevoir? Logically, it could only be accompanied with improved brake response. Improved brake response may mean better pedal feedback which in turn means better switch action. But it is still the responsibility of the BOO switch to illuminate the brake lamps.

My advice is to investigate the mechanics of the switch, the pivot bushings, the spring slide and the harness connection. After that if it still functions improperly, replace the switch.
 
RE: Brake light sendind switch

I, too, have complained about the brake light switch on my '97. The dealership checked it out for me. "No problem found."

I think that they are right. Although it is annoying, the reason that it seems to flash on-off-on-off so quickly is that the neon light is much faster to illuminate than the incandescent light bulbs that we're used to....maybe?

Ford has the right design here. The brake light is off the instant that the driver releases pressure from the pedal. Unfortunately, the spring on the switch is cautiously too strong for our sensitive brakes. I think that if the spring were softer, it would work better, but Ford usually errs on the side of caution.

If the brake light switch were mounted to the fire wall and attached with a link, it would not only require constant adjustment, it would not open the light circuit until the pedal returned to the full release position. Many drivers don't fully release the brake pedal although their intention is to cease decelerating and coast or increase speed. If the brake pedal isn't fully released in this setup the brake lights would remain on and it would be harder to tell when the car was actually decelerating. This would surely cause more rear-end collisions in traffic jams than a flickering brake lamp.

Between the flat side of the brake pedal arm and the flat plate of the switch there should be a little lubricant. This helps the switch to properly align with the pedal as gravity is working against it. Put a drop of oil there and it may help.
 
RE: Brake light sendind switch

Don’t bother changing the switch... there was another guy here that did the same thing, with no results.. that’s just how ford is.
 
RE: Brake light sendind switch


Don’t bother changing the switch... there was another guy here that did the same thing, with no results.. that’s just how ford is.
[/quote]


That person was probably me. Changed the switch - no difference. I didn't lubricate it, but there was a lot of grease still on the "pin" and the plastic bushing when I replaced it.

Dr. Dave, just to be clear, it's not just the neon light that goes out (at least on mine). It's all of them including the side lights.

Maybe the answer is a stiffer return spring for the brake cylinder piston. That's way out of my league though.

By the way, I don't remember how exactly, but the switch is kept in alignment by part of it resting on the brake pedal "lever" or whatever it's called. It doesn't hang down or anything. It's pretty much locked in position.
 
RE: Brake light sendind switch

I partially retract my earlier statement. Late yesterday evening in the garage, after checking for codes on my '93, I again played with the brakes watching the brake lamp reflection against the back wall of the garage. In response to recent posts in this thread I tried to emulate the symptoms.

I found if I deliberately partially released the brake pedal that the brake lamps would momentarily go out. It was as if the vacumn booster connecting rod had to 'catch up' to the retreating brake pedal. When ever I checked the lamp reaction to my normal application of the brake, the lamps simply came on when I pressed the pedal and went out immediately upon releasing the brake pedal. That's just the way I drive, I do not seem to modulate the brake pedal as evidently others do. I had to consciously change my brake application to get the brake lamps to be intermittent.

...but there was a lot of grease still on the "pin" and the plastic bushing when I replaced it.
...By the way, I don't remember how exactly, but the switch is kept in alignment by part of it resting on the brake pedal "lever" or whatever it's called. It doesn't hang down or anything. It's pretty much locked in position.
Click to expand...

Be cautious of too much grease as contamination of the switch contacts may occur.

Make sure the switch pivots freely and maintains alignment parallel to the push rod. The spring in the switch maintains axial alignment against the flat end of the push rod. If you push the pedal while watching the switch, it should change axially to the pedal while remaining straight with the push rod. The wire harness going to the switch should allow freedom of motion required.
 
RE: Brake light sendind switch

that swtich style looks very close to the ol fords my 79 f350 brake switch looks like that one ,if it is the same ,those do go bad ,i have replaced those , if i remember they did not cost much, still the same tech. after all these years
 
RE: Brake light sendind switch

I found if I deliberately partially released the brake pedal that the brake lamps would momentarily go out. It was as if the vacumn booster connecting rod had to 'catch up' to the retreating brake pedal.
Click to expand...

That's exactly the way my '97 neon brake light has always worked, and it kinda' makes sense to me they would design it like that. It gives a more accurate representation of the result of what the driver's actions really are, that you've increased your rate of travel compared to the initial deceleration, (so light comes off), even though overall you may still be decelerating. It makes a twisted sort of logic...

John
http://mark8.org/users/johnaec/Mark_VIII_s.jpg
'97 Mark VIII LSC
'96 T-Bird 4.6L
 
RE: Brake light sendind switch

I found if I deliberately partially released the brake pedal that the brake lamps would momentarily go out. It was as if the vacumn booster connecting rod had to 'catch up' to the retreating brake pedal.
Click to expand...

That's exactly the way my '97 neon brake light has always worked, and it kinda' makes sense to me they would design it like that. It gives a more accurate representation of the result of what the driver's actions really are, that you've increased your rate of travel compared to the initial deceleration, (so light comes off), even though overall you may still be decelerating. It makes a twisted sort of logic...

John
http://mark8.org/users/johnaec/Mark_VIII_s.jpg
'97 Mark VIII LSC
'96 T-Bird 4.6L
Click to expand...

I respectfully disagree. If my foot is on the brake pedal, the brake lights should stay on regardless of whether I'm easing up on it. After all, I'm still slowing down. If the guy tailgating me thinks I'm completely off the brake, he may do the same - then BANG. I realize it's usually just a split second that the lights are off, but hey.

It's dangerous, period. That, and I look like a friggin' old man who's riding the brakes. ;-)
 
RE: Brake light sendind switch

Oddly enough, there has been research into brake lights that change their response to the rate of deceleration. Usually by flashing faster with more G force. I just hope Ford isn't the first. LOL
 
RE: Brake light sendind switch

what i found with mine is that when i press the pedal sometimes they come on then go out while still pressing on the pedal,somtimes i press the pedal and they don't come on at all then i let up a little and they come on,I want to replace the switch btw the shift interlockthing works funny too! would you guys replace the module and how hard is it to?
 
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