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Discussion Starter · #1 ·
Hello all. Let me first start off by saying this is most likely self caused although not sure after the amount of trouble shooting I've done.

The project was to install front and rear cameras in my 2012 Mustang GT Roush S2 after putting in the Phoenix Automotive Tesla style 12" touch screen (installed no issues)

Installed rear camera and wired in no issues- tested a few times in reverse so I know the rear install didn't cause the issue.

Tested the front camera for power before wiring through the firewall of the car no issues. Had images displayed on head unit for both front and rear before starting the wiring through the firewall to the front of the car. Chose a rubber gasket to the left of the brake pedal that was already running a wire harness through the car. Used a screw driver and made myself a new hole in the gasket to run my camera wire through. Got the screw driver through what felt like 2 layers of rubber and ran my camera wire through. Unfortunately after getting the wire through the firewall trying to fish it through a tiny metal hole I ended up pulling too hard on the cable and broke the connector right at the base 🤦🏼‍♂️. (So now I'm waiting for a new camera to come in so I can just pull it through the reverse way,) but I went to pull the car into the garage and all of a sudden the car is stuck in park and I have no brake lights. So I go and do a lot of trouble shooting and as much videos as I can find on youtube saying it's most likely the brake light sensor. So This morning I go take a look and apparently I did knock it loose somehow while running the camera wire- I make sure the sensor is locked in place, try it, nada. I go back to videos and trouble shooting - maybe it's the fuse, suggested most likely 10amp- so I go check the interior fuse panel passenger side no busted fuses. I go buy a brand new brake light sensor for 40 and install it thinking this is gotta be it I must have broke the original- still nada 🤯. I have a test light and pulled the sensor off to check the pins on the male side of the plug that goes into the sensor; out of the 4 pins, one of them light up (not sure if that's how it supposed to be or not)

At this point I've done as much as I know how, I mean I don't know how I'm even having to deal with an issue with brake lights when I'm only running a wire from the radio through the firewall and up to the front of the car.

If anyone can help I appreciate it
 

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Probably blew the brake light fuse. You can’t shift out of park unless the brake circuit has power. Did you check the fuse panel under the hood and behind the passenger foot well panel?


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2014 GT, 1967 Fairlane GTA
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A bad, misadjusted, or improperly mounted brake light switch would cause this issue since the shift interlock depends on that switch working but since you put in a new switch another possibility is the shift interlock fuse may have blown or the shift interlock itself may have just failed.
The 2012 owner's manual: Ford (fordservicecontent.com)
The passenger compartment fuse panel has a Brake transmission shift interlock (BTSI) in fuse #5.
Rectangle Font Parallel Diagram Pattern

The power distribution box has a Brake on/off (BOO) power in fuse #24.
Font Parallel Number Rectangle Pattern

My guess is that when you blindly poked thru the firewall grommet that you may have penetrated into that harness and shorted out the brakes somehow. I'd go look for where that harness comes thru the firewall and inspect for damage.
 

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Discussion Starter · #5 ·
Ok so I posted some pictures so you all can see what I did and what I'm looking at. If you look at the wire going through the firewall gasket, you'll notice I tried to stay to the left of the actual harness going through. I don't believe I touched it but can't get a good look at it from the outside since there is sheet metal there and just a small oval of an opening.

I did some research and one video mentioned it could be a fuse so I did check the passenger side fuse panel but my panel was different than this persons 01 mustang. He mentioned his was a 10amp fuse for the brake light sensor for him so I checked all of the red 10amp fuses(interior passenger side) and all of them were good. I bought the Haynes manual (both digital and hardcopy) and unfortunately the wiring diagrams are only good for the 2005-2007 models so I could not find the accurate fuse panel diagram, etc. Thank you for providing that I will check those fuses next.
Other.
To answer Roachwe; I believe so, you can tell the plunger is pushed in when plugged up and when you press the brake I believe I can feel the plunger elongated so it seems to be working properly.

Also to not that the car does not throw any indicator lights or trouble codes so my Bama tuner doesn't have any DTC codes to view or clear.

Update: Fuse #24 and Fuse #5 are both good
Purple Toy Gas Electric blue Machine
Automotive tire Motor vehicle Hood Automotive fuel system Automotive exhaust
Automotive tire Military camouflage Electrical wiring Electric blue Fashion accessory
Guitar accessory Automotive tire Guitar Musical instrument Bumper
Tire Wheel Bicycle tire Automotive lighting Automotive tire
 

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Discussion Starter · #7 ·
Correct, I used the test light with the sensor pulled off and tested the 4 metal pins of the plug that connects to the sensor. I can try to test again when I get some time to see if when the brake is pressed if any other wires in that plug go hot, but the sensor will need to be plugged in and in place for that. I should be able to poke through the wires to check if any others light up and report back.

This sucks because there is literally no reason this should not be working at this point. All I did was drag a camera wire across the area. Everything else is working beautifully I just can't get the brake light sensor to work.

I will also check to see if what Cobrajet67 thinks might be the issue is correct (if I damaged the wires while poking through the rubber grommet) but I don't think I did. If you see the picture I posted, my camera wire is sitting to the left of the OEM wire bundle going through the firewall.

Any additional advice or help from anyone would be greatly appreciated!
 

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2014 GT, 1967 Fairlane GTA
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You have to test the switch itself. There may be room in the connector to get the probes to make contact with the tops of the pins with it connected to the switch. If not you could put on some temporary wire extensions from the connector to the switch. You really need a wiring diagram to tell you what goes where in order to understand what should be supplying power when the switch is engaged.
 

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See picture below... I think you should be seeing power on two of the circuits when the pedal is released and when the ignition is on (not power on just one circuit).
You should unplug the brake switch and jumper pins 1 and 4 on the harness side to see if the stop lamps illuminate, and if the trans can shift out of park, again with ignition on.


Also note that there is a right way and a wrong way to install the brake switch. If you install the switch while the pedal is depressed (like you are leaning on the pedal arm), then the switch can be damaged when the pedal is released, which essentially makes the plunger travel too far. The reason for the switch to be designed this way, is that the plunger length sets itself to the pedal dimensions when you insert and rotate the switch. That should be done with the pedal fully released in order for the brake lights to turn off when the pedal is released, and turn on when the pedal is barely depressed.
Brake_switch_installation_procedure
 

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Still wondering on jammed steering?? Happens with any car if wheels turned too far either way and ignition is shut off. Further turning in same direction just a tad will free that problem up. Just did that with my Boss last summer and that’s a 6 speed. Staying away on cameras…

Too these wiring harnesses are atrocious even in new autos, never would meet aircraft grade.
 

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The feeling of jammed steering when turned too far is caused by pressure being put on the steering column lock mechanism when torque is applied by the tires back through the system. The pressure on the lock mechanism makes it difficult to unlock the steering column. Putting pressure on the steering wheel with your hands relieves that pressure on the lock mechanism. Parking with wheels straight / relaxed should avoid this issue. Totally unrelated to the brake switch / trans shift interlock topic.
 

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Discussion Starter · #12 ·
See picture below... I think you should be seeing power on two of the circuits when the pedal is released and when the ignition is on (not power on just one circuit).
You should unplug the brake switch and jumper pins 1 and 4 on the harness side to see if the stop lamps illuminate, and if the trans can shift out of park, again with ignition on.


Also note that there is a right way and a wrong way to install the brake switch. If you install the switch while the pedal is depressed (like you are leaning on the pedal arm), then the switch can be damaged when the pedal is released, which essentially makes the plunger travel too far. The reason for the switch to be designed this way, is that the plunger length sets itself to the pedal dimensions when you insert and rotate the switch. That should be done with the pedal fully released in order for the brake lights to turn off when the pedal is released, and turn on when the pedal is barely depressed.
Brake_switch_installation_procedure
  • To be clear, you are saying that there should be power to 2 of the circuits when the pedal is released (*meaning the plunger of the sensor is pressed in, correct?)
  • Second thing to get clarity on is what you mean by jumper pins?(the wires going into the white plug that plugs into the sensor?) Which colors should they be, because the diagram you show me has different colored wires(please see my reference photos previously Posted) The wire getting power(test light lit up) is the green/yellow striped wire. There are 2 other purple (or purple/white striped) wires on the ends and then one black/blue striped wire.
  • 3rd thing are you saying to unplug these jumper pins 1 and 4(please advise on colors) and do nothing else and the brake lights should come on and I should be able to move from park? Or after unplugging jumper pins then reconnect sensor and put in position and try to work the brake pedal to get lights/shift from park?
Also note that I did not move the pedal position while installing the sensor and did not press the brake pedal until after the sensor was installed.
 

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Discussion Starter · #13 ·
You have to test the switch itself. There may be room in the connector to get the probes to make contact with the tops of the pins with it connected to the switch. If not you could put on some temporary wire extensions from the connector to the switch. You really need a wiring diagram to tell you what goes where in order to understand what should be supplying power when the switch is engaged.
To be clear you are calling the brake light sensor the "switch" correct?
My question to that is I've already bought and replaced the sensor/switch itself. Why would a brand new sensor not work unless I blew a fuse? Fuses are good though.

With the sensor plugged into the white connector male piece (4 pinned/wired plug) there is no room to get a test light to the tabs that go into the sensor (the sensor covers them completely) except maybe from the backside of the plug on the wire side I could try to test. But again not even sure what I'd be testing for other than to see if one other wire is hot. If it is and still not allowing me to shift or have lights, what do I do then? If not, what do I do then?? Lol
 

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Yeah, it is a switch, not a sensor. A plunger switch. The schematic shows that there are two sets of contacts inside... one is normally closed and one is normally open when the pedal is released. Then when you press the pedal (and extend the plunger) then both contacts change states.

Ignore the wire colors, as that schematic is actually from the F150 manual. But the switch is the same, and the way it is wired is the same. I think if you look closely, you can see that the connector pins are numbered 1 through 4. For sure, they will go in order, so when looking into the connector, it will either be 1-4 left to right, or right to left... one or the other.

If you unplug the switch and test it with a multimeter set to ohms (resistance, or continuity), then you can quickly figure out which pins are which. With the plunger depressed, you can see that pins 2 and 3 should have continuity, and pins 1 and 4 should be open. When you release the plunger, then pins 1 and 4 should have continuity and pins 2-3 should open. This quick test can be done to not only verify that the switch is functioning, but also to verify which pin is which. Once you know the pinout on the switch side, then you also know which pin is which on the harness side.

On the harness side, with the harness unplugged from the switch, you should measure power on both pins 1 and 2. I suspect you are getting power on only one of these circuits. You can also measure resistance to ground on pin 3 of the harness side connector. The schematic shows that pin 3 should be ground, so if you use a multimeter and measure resistance between harness pin 3 with one probe and touching a good ground with the other probe, you should see nearly zero ohms of resistance. If you see an open circuit or high resistance, then look for trouble along harness circuit number 3.. maybe you cut it or pulled the wire or pin out of the connector or something. If you don't have power on either pins 1 or 2, then look at those circuits for damage or pins that pulled out. If possible, look on the other side of the dash panel, because that is where you were poking around and may have hit something on the other side.

If you get power on pins 1 and 2, and ground on pin 3 when the harness is unplugged, then you can try jumpering the pins to see what happens. Jumpering means to use a short piece of wire or maybe a paper clip to make electrical contact between two of the pins, while the harness is still unplugged. You are essentially simulating what the switch will be doing when you press and release the pedal. Jumpering pins 1 and 4 on the harness side will simulate pressing the pedal, and it will send power from pin 1 over to pin 4 which goes to the Body Control Module. The body control module then illuminates the stop lamps when it sees power on pin 4. So, jumpering pins 1 and 4 should make the stop lamps come on. I'm not 100% sure if the BCM or the PCM has the task of controlling the brake shift interlock mechanism for letting you shift out of park. Jumpering pins 2 and 3 simulates the release of the brake pedal, and NO JUMPER on pins 2 and 3 simulates pressing the pedal. So.. just put a jumper on pins 1 and 4 and it should simulate pressing the pedal.. see what happens. If you have power on pins 1 and 2, and pin 3 has a good ground, and jumpering pins 1 and 4 does not light up the stop lamps, then you should suspect something wrong in the circuit to pin 4.

Based on what work you've done, you most likely damaged a circuit since you were working in that area. But if all circuits are truly ok, then perhaps there is a functional issue with either the BCM or PCM, but it seems unlikely.

To perform tests while the harness is plugged into the switch, you can "back probe", which means to insert your probe into the back side of the connector where the wire enters the connector. If your probe is too fat, you can insert a needle or some other thin wire down into there until it makes contact with the terminal, then touch your probe to that wire or needle.
 

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To be clear you are calling the brake light sensor the "switch" correct?
My question to that is I've already bought and replaced the sensor/switch itself. Why would a brand new sensor not work unless I blew a fuse? Fuses are good though.

With the sensor plugged into the white connector male piece (4 pinned/wired plug) there is no room to get a test light to the tabs that go into the sensor (the sensor covers them completely) except maybe from the backside of the plug on the wire side I could try to test. But again not even sure what I'd be testing for other than to see if one other wire is hot. If it is and still not allowing me to shift or have lights, what do I do then? If not, what do I do then?? Lol
Yes, I am since the industry refers to this part as a switch and not a sensor: 2007-2021 Ford Switch GL3Z-13480-A | TascaParts.com
 

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Discussion Starter · #17 ·
Yeah, it is a switch, not a sensor. A plunger switch. The schematic shows that there are two sets of contacts inside... one is normally closed and one is normally open when the pedal is released. Then when you press the pedal (and extend the plunger) then both contacts change states.

Ignore the wire colors, as that schematic is actually from the F150 manual. But the switch is the same, and the way it is wired is the same. I think if you look closely, you can see that the connector pins are numbered 1 through 4. For sure, they will go in order, so when looking into the connector, it will either be 1-4 left to right, or right to left... one or the other.

If you unplug the switch and test it with a multimeter set to ohms (resistance, or continuity), then you can quickly figure out which pins are which. With the plunger depressed, you can see that pins 2 and 3 should have continuity, and pins 1 and 4 should be open. When you release the plunger, then pins 1 and 4 should have continuity and pins 2-3 should open. This quick test can be done to not only verify that the switch is functioning, but also to verify which pin is which. Once you know the pinout on the switch side, then you also know which pin is which on the harness side.

On the harness side, with the harness unplugged from the switch, you should measure power on both pins 1 and 2. I suspect you are getting power on only one of these circuits. You can also measure resistance to ground on pin 3 of the harness side connector. The schematic shows that pin 3 should be ground, so if you use a multimeter and measure resistance between harness pin 3 with one probe and touching a good ground with the other probe, you should see nearly zero ohms of resistance. If you see an open circuit or high resistance, then look for trouble along harness circuit number 3.. maybe you cut it or pulled the wire or pin out of the connector or something. If you don't have power on either pins 1 or 2, then look at those circuits for damage or pins that pulled out. If possible, look on the other side of the dash panel, because that is where you were poking around and may have hit something on the other side.

If you get power on pins 1 and 2, and ground on pin 3 when the harness is unplugged, then you can try jumpering the pins to see what happens. Jumpering means to use a short piece of wire or maybe a paper clip to make electrical contact between two of the pins, while the harness is still unplugged. You are essentially simulating what the switch will be doing when you press and release the pedal. Jumpering pins 1 and 4 on the harness side will simulate pressing the pedal, and it will send power from pin 1 over to pin 4 which goes to the Body Control Module. The body control module then illuminates the stop lamps when it sees power on pin 4. So, jumpering pins 1 and 4 should make the stop lamps come on. I'm not 100% sure if the BCM or the PCM has the task of controlling the brake shift interlock mechanism for letting you shift out of park. Jumpering pins 2 and 3 simulates the release of the brake pedal, and NO JUMPER on pins 2 and 3 simulates pressing the pedal. So.. just put a jumper on pins 1 and 4 and it should simulate pressing the pedal.. see what happens. If you have power on pins 1 and 2, and pin 3 has a good ground, and jumpering pins 1 and 4 does not light up the stop lamps, then you should suspect something wrong in the circuit to pin 4.

Based on what work you've done, you most likely damaged a circuit since you were working in that area. But if all circuits are truly ok, then perhaps there is a functional issue with either the BCM or PCM, but it seems unlikely.

To perform tests while the harness is plugged into the switch, you can "back probe", which means to insert your probe into the back side of the connector where the wire enters the connector. If your probe is too fat, you can insert a needle or some other thin wire down into there until it makes contact with the terminal, then touch your probe to that wire or needle.
That's extremely helpful but over my head a little. I understand a lot of that but probably not enough to be able to follow this and do it on my own. I don't have a volt meter only a test light.

This is specifically the part I wouldn't know my head from my ass on:
"If you see an open circuit or high resistance, then look for trouble along harness circuit number 3.. maybe you cut it or pulled the wire or pin out of the connector or something. If you don't have power on either pins 1 or 2, then look at those circuits for damage or pins that pulled out. If possible, look on the other side of the dash panel, because that is where you were poking around and may have hit something on the other side."

Anyone by chance in Denver and want to give me a hand before I have it towed to the Ford dealership? lol
 

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Sorry about that. Open circuit simply means a broken wire somewhere... the circuit is interrupted. High resistance is where the circuit is intact, but perhaps a damaged wire, or partial connection, or corrosion at the terminal... anything that can impede the flow of electricity, but still allow some electrical contact.

Without following the troubleshooting ideas above, the best suggestion would be to double check then triple check the wires in the area where you were poking and yanking and visually inspect for damage. It can be hard to tell since wires are in a bundle and concealed by surrounding wires, and a terminal that gets partially pulled out of the connector can be impossible to see unless you know exactly where to look.

If nobody in your area is able to help you troubleshoot, you can over-ride the shift interlock solenoid to get the vehicle out of park and be able to drive it, but you still won't have brake lights. This would let you get to a repair shop without a tow truck, assuming they are close enough that you can drive there safely without brake lights. Not that I would recommend this!! But if you do, you might have a friend follow directly behind you, so nobody else would rear-end you due to lack of brake lights.
This video shows how to reach the shift interlock solenoid... https://www.youtube.com/BTSI_override
 

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Discussion Starter · #19 ·
I did stumble across the shift interlock override video while trying to find info on my own, and that might be my next resort to just have my wife follow me and take it to Ford.
I have off today so I will go pick up a multimeter and try the things you have suggested and go from there.
Thanks again for taking the time out of your days with all the help guys, especially Brent72 and Cobrajet67, really appreciate it!
 
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