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1994 SR5 4x4 New brake light switch now lights go out when pedal is pressed

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1994 SR5 4x4 New brake light switch now lights go out when pedal is pressed

Old 05-15-2019, 08:40 AM
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1994 SR5 4x4 New brake light switch now lights go out when pedal is pressed

Hi everyone! I am hoping with all of our awesome collective gearheads available to this forum, I can get this maintenance done. My question is below. Anyway, I was told, in a not so friendly manner, that my brake lights (on both sides) were not working. Interestingly, my cruse control stopped working awhile ago. My truck is a 1994 SR5 4x4, A340H, 3VZE, Cruse Control, A/C, Xcab, etc...basically all the bells and stuff.

When I press the brake pedal with headlights and running lights on I get no brake lights to either side, none. And, the rear running lights go out. With the headlight switch in the off position and no key in the ignition, I press the brake pedal, no brake lights.

All of the fuses in the fuse box on the drivers side all turned up okay on testing with the fuse puller test function. All got a green light. This is pointing to a bad brake light switch. It's original to the vehicle. A real bugger to remove. If anyone wants to how I got the switch out, please let me know. It may not be the factory sequence, but it worked.

I merely plugged the new switch into the harness. I purposely did not mount the new switch, just plugged it in to see if it the situation improved by simply pressing or not pressing, by hand, the new switch plunger to see how the lights were functioning. On simply plugging in the harness to the new switch, my third brake light and both running lights are illuminated and I get that "lights left on" warning squeal when go to leave your car but you left the headlights on kind of squeal, you the one. Now, when I press the new switch, by hand, to close the circuit, which means the brake lights should illuminate, all the lights go out. This is the opposite of what should be happening. All I did was to swap out the brake light switch, NOTHING else. Could I have a bad headlight switch??

Any info is appreciated. Signed, Chezdwilly, pronounced ShadyWilly
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Old 05-15-2019, 03:33 PM
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Most brake light switches are such that when you let off of the pedal it comes up and pushes on the switch plunger, like you are doing with your finger, so it is working as it should. You press the button the lights go off.
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Old 05-15-2019, 03:43 PM
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Like akwheeler said, your switch is working correctly.

This is what is called a normally closed switch, meaning if nothing is pushing on it, the contacts inside the switch close.

If you look on how the switch is mounted, the brake pedal pushes the switch in its "resting" position, which keeps the brake lights off most of the time. When you step on the brakes, the brake pedal and the switch stop making contact, the switch gets pushed out by the spring inside of the switch, the contacts inside the switch make contact, and the brake lights come on.

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Old 05-15-2019, 05:15 PM
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Originally Posted by old87yota View Post
Like akwheeler said, your switch is working correctly.

This is what is called a normally closed switch, ...:
Originally Posted by chezdwilly752 View Post
.. my cruse control stopped working awhile ago. ...

When I press the brake pedal with headlights and running lights on I get no brake lights to either side, none. And, the rear running lights go out. ...
....
On simply plugging in the harness to the new switch, my third brake light and both running lights are illuminated and I get that "lights left on" warning squeal ... when I press the new switch, by hand, ... all the lights go out. ...
Elementary, my dear Watson. Well, once we get some more clues. old87yota and akwheeler are correct about the normal operation of the switch. Here's a drawing of how it's installed to help http://web.archive.org/web/201203161.../3checksan.pdf (and as you can see, it shouldn't have been that difficult to remove ... which itself is another clue.)

The brake light switch is a dual switch (four leads). The other half of the switch controls Cruise, so if the switch failed closed Cruise would stop working.

So what's up with the taillights? The brake and taillights use a single bulb with two filaments. If you had a broken ground wire (the common wire to the bulb) AND a brake switch that shorted to ground, the brake switch would switch BOTH filaments. With the brake switch restored as you did, the brake light circuit might illuminate both filaments, switching them off when you press the switch. And if you are now powering the tail lights, you'll activate the lights-on reminder.

But this is all still mysterious until we know more. Remove one tail-light lens so you can see both filaments. With hand off the brake switch and lights off, do either filament light? Both? Press the switch and record what you (your assistant) sees. Repeat these two steps with the tail lights on.

And since someone else will ask, do you have a trailer harness?
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Old 05-15-2019, 05:39 PM
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Originally Posted by scope103 View Post
Elementary, my dear Watson. Well, once we get some more clues. old87yota and akwheeler are correct about the normal operation of the switch. Here's a drawing of how it's installed to help http://web.archive.org/web/201203161.../3checksan.pdf (and as you can see, it shouldn't have been that difficult to remove ... which itself is another clue.)

The brake light switch is a dual switch (four leads). The other half of the switch controls Cruise, so if the switch failed closed Cruise would stop working.

So what's up with the taillights? The brake and taillights use a single bulb with two filaments. If you had a broken ground wire (the common wire to the bulb) AND a brake switch that shorted to ground, the brake switch would switch BOTH filaments. With the brake switch restored as you did, the brake light circuit might illuminate both filaments, switching them off when you press the switch. And if you are now powering the tail lights, you'll activate the lights-on reminder.

But this is all still mysterious until we know more. Remove one tail-light lens so you can see both filaments. With hand off the brake switch and lights off, do either filament light? Both? Press the switch and record what you (your assistant) sees. Repeat these two steps with the tail lights on.

And since someone else will ask, do you have a trailer harness?
Good suggestion on the trailer harness Scope, Also I have seen people put the wrong bulbs in and get interesting results.
OP, if your brake light switch doesn't fix your problem you should also pull your brake light bulbs and make sure they are not 1156 bulbs installed where they should be 1157, I think that's what is supposed to be there.
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Old 05-16-2019, 08:30 AM
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Hi AKWheeler and All,

Thank you for all of the information. I'm just now reading your reply. I tried again yesterday morning. Inserted the switch back into the harness and this time, silence. Which is what I was expecting the first time around. You guys are correct. It turns out that the switch has a "sweet spot" that I had to find in adjusting the darn thing. I had to run the plunger pretty far into the switch. Much farther than I thought. I think the manu's are supposed to preset the distance of the lock-nut. Hum... The fix was simple. Access to the unit, not so simple. Have you ever noticed that it seems like you have to have pretty small hands to work on these things?! (Yuk! Yuk!) The top of my left hand and wrist are especially is hammered.
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Old 05-16-2019, 10:46 AM
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Originally Posted by chezdwilly752 View Post
Have you ever noticed that it seems like you have to have pretty small hands to work on these things?! (Yuk! Yuk!)
I practice by building ships in bottles, once you get the hang of working through a 1" hole with chopsticks it's no problem!
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Old 05-16-2019, 01:36 PM
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Originally Posted by akwheeler
I practice by building ships in bottles, once you get the hang of working through a 1" hole with chopsticks it's no problem!
With that skill want to come over and fix my tailgate crap so I dont have to jump my rear window switch to get it to work.
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Old 05-16-2019, 02:05 PM
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Originally Posted by thefishguy77 View Post
With that skill want to come over and fix my tailgate crap so I dont have to jump my rear window switch to get it to work.
Washington and Alaska aren't getting any closer together any time soon, show up on the Kenai Peninsula for summer fishing like all the other tourists and I'll be happy to help you out.
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Old 05-16-2019, 04:33 PM
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Originally Posted by akwheeler
Washington and Alaska aren't getting any closer together any time soon, show up on the Kenai Peninsula for summer fishing like all the other tourists and I'll be happy to help you out.
That would be a long haul in the runner. Would have been a great road trip in my 20's
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Old 05-17-2019, 09:06 AM
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Dude! That's freaking hilarious!!
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Old 05-17-2019, 09:12 AM
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Given the physical size of my little (oxymoron?) truck...on those big ol' roads in the northwest, I wonder if my Ford F-150 Super Crew would have a hard time fitting on the roads over yonder?? I'm just kidding, of course it wouldn't fit.....
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Old 05-17-2019, 09:26 AM
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Scope103,

Right on! for the information. I have printed this out and added it to me manuals. This is the kind of detail and knowledge that really help out.
Thank You!
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Old 05-17-2019, 09:32 AM
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Why, yes, I do have a trailor harness. I did have a nice boat to pull it with too. But not after, well....at least I'm single.
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