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Vive Les Revolucion!
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Alright, lets skip the "why would you want to disable your brake lights?" questions by stating that I have very specific reasons for desiring this, and should a mod want to know, they can PM me. And to be fair (yes, I did just start a sentence with "and") its also a curiosity in my mind of just how monitored are the "safety" systems?

NOW, that out of the way, Is it possible to disable the brake lights on the mk3 focus? What I mean is, if I were to cut power, would it disable the brake lights without affecting the rest of the vehicles electronics? or would it cause the BCM to "freak out" when the power to a safety system disappears?

As for how to accomplish this, Im also open to suggestions, as my current thought process is to either:

A) Use a pair of fuse taps and a dead fuse as a "bypass" of sorts (yes, it would still be fused to the correct amperage, but would be connected to a relay to provide the shutoff function)...

B) Cut the brake switch power feed between fuse panel and switch and add the relay there.

C) Use the relay to switch the load to a pair of resistors of appropriate resistance, thereby "fooling" the computer into thinking the system is functioning correctly (assuming that cutting power would generate major errors).

Relay would be of a Normally Closed variety (or 5-pin). Again, would this generate more than the relatively simple "brake light out" error?
 

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Whatever you're doing it sounds illegal.
 

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Vive Les Revolucion!
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Discussion Starter #3

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I didn't ask "why would you want to disable your brake lights". Why not just take out the bulbs?

 

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I assume you work security and want to run in full stealth mode with no lights at times?

Why not just wire in a DPDT switch into the wiring feeding the brake lights and throw the switch when you want to be stealth. The computer would just see that as burned out bulbs until you throw the switch back to the on position.

Disclaimer: Please don't do this! I do not recommend or endorse it.

because then the car would not be road-legal?
Technically, any method of disabling the brake lights would be illegal and possibly life threatening. At least you would have a visual indication in the cockpit that you had a burned out bulb and remember to switch the brake lights back on.
 

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Vive Les Revolucion!
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Discussion Starter #6
I didn't ask "why would you want to disable your brake lights". Why not just take out the bulbs?
because then the car would not be road-legal?
 

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Vive Les Revolucion!
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Discussion Starter #7
I assume you work security and want to run in full stealth mode with no lights at times?

Why not just wire in a DPDT switch into the wiring feeding the brake lights and throw the switch when you want to be stealth. The computer would just see that as burned out bulbs until you throw the switch back to the on position.

Disclaimer: Please don't do this!
thats what Im wondering... My google-fu seems to indicate that the car won't start if the brake lights are nonfunctional... Im also wondering if the electronics would kick the car into "limp-home" mode if the brake switch lost power... I want to know if the car will freak out before attempting something like this...
 

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This is easily the stupidest thing I've ever seen posted on a message forum. Unless the vehicle is being used for off road purposes there is no way on earth there is a good reason to disable your brake lights. Good God man
 

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Discussion Starter #9
This is easily the stupidest thing I've ever seen posted on a message forum. Unless the vehicle is being used for off road purposes there is no way on earth there is a good reason to disable your brake lights. Good God man
 

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Discussion Starter #10
Technically, any method of disabling the brake lights would be illegal and possibly life threatening. At least you would have a visual indication in the cockpit that you had a burned out bulb and remember to switch the brake lights back on.
Well, the switch that would be used (should it be found to be possible) would have a small indicator connected to it (dimmed as necessary), so that would provide the indication, but I do understand and appreciate your help.
 

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One way to do it and not have to worry about any sort of computer stuff is to have the switch cutting the lights also have a dummy load equal to the current used by the brake and/or running lights.
So you have a switch cutting power to the actual lights in back, (and NOT the brake switch which is used for starting the car etc_)
The switch would have to be multi pole to cover both sides, and double throw so on switch , one side brake lights connected, the other side dummy load faking brake lights
A couple of 10 watt resistors bunched up until you have an effective load which will not overheat. Or even real brake light bulbs placed in a sealed metal box will do.
You would want a ohmmeter etc to check the load, and the dummy load, and check how hot your dummy load is getting (so no fires. nothing like a car fire to spoil your stealth mode) [hah]

A one switch one wire to the back of the car solution would be switch at dash, HOT wire to rear with relay/relays at each spot cutting from brake light to dummy load.
One relay? or whatever, the lights would be on normally then flip switch hot 12V hits relay/relays and the dummy load gets the brake signal instead of the 3 brake lights.

Why this person wants to do this is not my problem. The answer can help? great.
 

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To be honest the easiest way I would think is to add lights into the trunk to avoid resisters. And like others have said use the relay to separate the circut for it.

As far as legality lots of stuff posted on the forum is illegal or not recommended. Hids in stock housings or window tint etc etc. Instead of just telling the op to not do it just don't post. You don't know why he needs too do it so just reply with useful info or move to the next post to troll.
 

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Discussion Starter #13
Thank you to both! I'm thinking a pair of 6ohm 50watt resistors will do exactly what I'm looking for without having to worry about messing with the rest of the wiring harness. They are normally used to fix hyper-blinking after installing LED signal bulbs, so they should work just perfectly! Again, thank you for your help!
 

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If you have LED brake lights you can just use one of these electro shocker thingies on the LED light bulbs, that should destroy them pretty fast. Ya know one of These thingies ladies have in their Hand bags to fend off bad dudes. Then you can just plug the LED lights back in and be like "Awww no idea why all of them faield at once, must be chinese Quality..."
 

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Cut the brake wire at the BCM and use a relay to activate. I do it everyday on police cars.
 

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Vive Les Revolucion!
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Discussion Starter #17
new cars? or old vic's? or both?

You mean cut the output wire from the bcm to the switch, correct?
 

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Discussion Starter #19
Good to know! Thank you!
 

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I want to do this as well as be able to kill all of my interior lights.. [ninja]
 
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