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1992 Ford Eddie Bauer Bronco 5.0
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Discussion Starter · #1 ·
So I had my transmission rebuilt this week. Keep. Keep in mind I had the original rebuilt twice and it failed. Installed a used transmission about year and 1/2 ago and it went out last week. Took it to a shop with "good reviews" and they told me that think the third brake light was the issue. They said that since it was melted, it might have been sending a signal to the computer that I was applying the brake thus cause the converter not to enage. They removed the third brake light and rebuilt my burned out transmission. My question is could a bad third brake cause the computer to think I was applying the brake and messing with the signals? I'm picking my baby up this weekend when I get paid.
 

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85 Bronco, 309ci I6 w/4bbl, np435, 4" lift, 37" Irok NDs, 4.56 w/ Detroit Locker and tru trac
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I have no clue. But I had my 94 top off many times with the light disconnected and no issues.
 

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Yes.

I was pulling my trailer and the filament in the bulb for the running lights broke and was bouncing onto the brake light filament (same bulb) . Torque converter kept disengaging.

Turned off running lights, and all was fine.
 

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1992 Ford Eddie Bauer Bronco 5.0
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Discussion Starter · #4 ·
Well I hope that is the issue but if that was my problem all along, Im kind of pissed. Replacement third brake light like under $100 and I am out $3k again over a small ass part costing me thousands of dollars
 

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Ford failed to properly isolate the BOO (Brake On/Off) circuit for the EEC in the Bronco(s) and F-150s.

On non 3 brake light vehicles installing LEDs and or having a Burned out bulb can send power to the BOO circuit and keep the torque converter from functioning properly allowing the transmission to get hot and could allow it to burn up with enough driving.

On 3rd Brake light Bronco(s) and F-150s the left and right Brake bulbs don't matter as much but the 3rd bulb does. Having a LED or Blown bulb can allow power to ativate the BOO circuit even when your not activating the Brake switch. I don't have any knowledge that a missing bulb can cause an issue (aka taking the top off) but I have heard from some '96 owners that a missing bulb does cause shifting issues.
 

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Yes, an issue with the 3rd brake light will cause transmission issues.

It tells the computer that the brake is being pressed. If you have cruise control, I imagine it doesn't work either because it thinks you're pressing the brake.

I don't have a 3rd brake light, but did a bunch of research on Ford's brake light system when I converted my Bronco to LED. It uses the bleed off of the voltage through the bulbs to know if the brakes are pressed or not. When I did LEDs, there wasn't enough bleed off into the bulb due to their low voltage usage, so it always thought the brakes were pressed. I learned about it by reading about how people would leave a single halogen bulb in the 3rd brake light to take care of it. People who put all LEDs into their brake lights (including the 3rd) had transmission shifting issues.

Unplugging the 3rd brake light is different, as it disconnects the circuit entirely.
 

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85 Bronco, 309ci I6 w/4bbl, np435, 4" lift, 37" Irok NDs, 4.56 w/ Detroit Locker and tru trac
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Wow... Learn something every day
 

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Yes, an issue with the 3rd brake light will cause transmission issues.

It tells the computer that the brake is being pressed. If you have cruise control, I imagine it doesn't work either because it thinks you're pressing the brake.
Same thing with a broken filament wire inside the light bulb. If it's energized and then rests on the brake light filament, it tells the computer the brakes are being applied.
 

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'92 Custom w/ '95 MAF 5.0 M/T, 33's, 4.10 LSD
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Weird...and educational.

I put LED bulbs in my 3rd brake light, after looking at spares and seeing they had all been pretty badly melted by incandescents. I never had any issue as a result, at least not that I was aware of, but maybe my system is simplified having no cruise. I've since switched from E4OD to M5OD, which probably further simplifies that situation.
 

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I put LED bulbs in my 3rd brake light, after looking at spares and seeing they had all been pretty badly melted by incandescents. I never had any issue as a result, at least not that I was aware of, but maybe my system is simplified having no cruise. I've since switched from E4OD to M5OD, which probably further simplifies that situation.
Yup, a manual with no cruise will never know the difference. :D

However, if you ever do the same with your turn signals, you'll run into the same issue. It uses the voltage to heat up the "clicker" inside the turn signal fuse, which the LEDs won't do.
 
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1992 Ford Eddie Bauer Bronco 5.0
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Discussion Starter · #11 ·
Yes, an issue with the 3rd brake light will cause transmission issues.

It tells the computer that the brake is being pressed. If you have cruise control, I imagine it doesn't work either because it thinks you're pressing the brake.

I don't have a 3rd brake light, but did a bunch of research on Ford's brake light system when I converted my Bronco to LED. It uses the bleed off of the voltage through the bulbs to know if the brakes are pressed or not. When I did LEDs, there wasn't enough bleed off into the bulb due to their low voltage usage, so it always thought the brakes were pressed. I learned about it by reading about how people would leave a single halogen bulb in the 3rd brake light to take care of it. People who put all LEDs into their brake lights (including the 3rd) had transmission shifting issues.

Unplugging the 3rd brake light is different, as it disconnects the circuit entirely.
You are 100% correct my cruise does not work and I have replaced all the fuses and relays for the cruise.

What would you recommend I install as a third brake light that wont melt. Also what other lines should I be looking at to ensure I am not sending a false positive to the system. This seems like such an small odd thing that can do some real damage. I never would have imagined that my rear third brake light might be the cause of all my busted transmissions.
 

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1995 5.8, 2.5" Rough Country Lift, Extended RA's, 4.10's, 33" BFG's
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I have been daily driving my 95 for 11 years and the third brake light never worked and I've never had transmission problems.
 

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1992 Ford Eddie Bauer Bronco 5.0
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Discussion Starter · #13 ·
I have been daily driving my 95 for 11 years and the third brake light never worked and I've never had transmission problems.
Glad to hear that but I on the other hand have had two rebuilt transmission go out and a used one burn out as well. This will be my 4th transmission job done in 8 years. And if it is the third light, I want to say to the Ford engineers, get f'ed. A small ass part such as a third brake light should not mess with the transmission.
 

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'92 Custom w/ '95 MAF 5.0 M/T, 33's, 4.10 LSD
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You know, now that I think about it...half of my reason for doing the M/T swap is my E4OD was starting to slip while towing/hauling. It never occurred to me that could be 3rd brake light related.

Regardless, @sadboy , I feel your pain and disdain. Part of the other half of my reason for the M/T swap is a general distrust of Ford's electrical know how of the day. This situation certainly reinforces that.
 

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Discussion Starter · #15 ·
Well if my rebuilt transmission goes out again, I am going to looking into doing a swap if it is even possible
 

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You are 100% correct my cruise does not work and I have replaced all the fuses and relays for the cruise.

What would you recommend I install as a third brake light that wont melt. Also what other lines should I be looking at to ensure I am not sending a false positive to the system. This seems like such an small odd thing that can do some real damage. I never would have imagined that my rear third brake light might be the cause of all my busted transmissions.
Give my #7 post here a read about LED wiring.

Another trick I used is a manual F150 is a "25ohm 50watt" resistor on the lights side of the Brake switch wiring, and put the other end of the resistor to ground.
 
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Yeah, it does seem to be an oversight on their part. It really should have only been tied directly to the switch on the brake pedal.

I think your issue is with what is causing it to melt. Something else is going on that's doing that, such as a short in the system somewhere, and it's affecting the brake circuit too.

what years does the faulty 3 rd brake light affect the tranny, abd goes it also affect the f 250s?
The 3rd brake light was in 92 - 96 Broncos. I don't know if the f-series had it yet on the cab, but maybe.
 

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95 5.8L MAF XLT, Hedman Shorties/MF SS Y & Muff, E4OD, Man hubs, KYB Quads, 31x10.5x15, 304K miles
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Another thing that causes the Transmission to go in and out of Lock-up is the Warning Flashers, every time they Flash on the Torque Converter unlocks and when they go off it wants to Lock-up again. So if you drive with your Flashers on for some "Emergency" reason you are not doing your Trans any Favors. Just some more FYI stuff!
 

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Glad to hear that but I on the other hand have had two rebuilt transmission go out and a used one burn out as well. This will be my 4th transmission job done in 8 years. And if it is the third light, I want to say to the Ford engineers, get f'ed. A small ass part such as a third brake light should not mess with the transmission.
I think it is more of an unintended consequence issue. and a combination of saving some money by not adding in another relay circuit. I find it somewhat laughable and humorous, although I really feel for the pain and expense it has put you through, I've been dealing with similar issues on one of my trucks (something small and innocuous costing me thousands of dollars in repairs before we finally found the real culprit...)
 
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