'2012 Ford F750 Brake Lights Not Working - Diesel Forum - TheDieselStop.com
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post #1 of 17 (permalink) Old 06-05-2018, 09:47 AM Thread Starter
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Question '2013 Ford F750 Brake Lights Not Working

Ok so I have a 2013 Ford F-750 with a Cummins Diesel. The issue is that when the brakes are applied, the brake lights do not illuminate! Now here's the kicker, I work for a Truck Fleet and we DO NOT have any schematics or wiring diagrams so we are working blind on this. We have tested all the wiring from the lights all the way to the relays and fuses and have continuity. We even applied power directly to the lights themselves and they work. All other lights are functioning to include the parking lights. We check the switch at the pedal and even swapped it for shi+s and giggles and still nothing. We tested the relays and checked the fused and everything seems fine. ANY HELP would be greatly appreciated...I'm at the end of my nerves with this issue. TIA.

Last edited by BTRfleetTech; 06-07-2018 at 02:28 PM.
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post #2 of 17 (permalink) Old 06-05-2018, 09:58 AM
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This may not be much help, but when I'm doing electrical diagnostics, I try to break the circuit into pieces to try to isolate a segment at fault. I would start at the brake switch. I would check for 12 volts on one leg. If you don't have power to the switch, then I'd go looking for why. If you do, then I'd jumper the connector and see if the brake lights came on. If they do, then the switch (or it's adjustment) is at fault. If they don't, then the problem is between the connector and the switch. Let's say they didn't come on. Then, I'd find the connector near the rear bumper that the frame wire connects to where it splits to the two sides. Check for power there when the brake switch is applied. Yes - problem is further downstream. No - problem is between the switch and that connector. By halving your area of interest each test, you'll eventually get it narrowed down to a specific spot.

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I wonder if clouds ever look down on us and say, "Hey, look - that one is shaped like an idiot!"
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post #3 of 17 (permalink) Old 06-05-2018, 10:33 AM Thread Starter
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Thanks for the advice man
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post #4 of 17 (permalink) Old 06-06-2018, 03:53 PM Thread Starter
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Still not having any luck with this issue.. I checked the cable that goes to the brake light switch and none of the connectors have any voltage. What I need to know is where does that cable get voltage from, passenger side junction box or outside driver side junction box. Better yet, if anyone has any wiring diagrams that would help even more.. THANKS
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post #5 of 17 (permalink) Old 06-06-2018, 07:22 PM
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AIR or HYDRAULIC brakes?


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post #6 of 17 (permalink) Old 06-06-2018, 07:55 PM
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Oh, before you go nuts, do us both a favor and exercise the hazard switch on the top of the steering column. Turn them on and off a dozen times and wiggle the button a little. Then see what works. The hazard part of the multifunction switch tends to gather dust and God knows what other crap that causes the contacts to foul. The stop lamp circuit runs through the multifunction switch. If doing that corrects the stop lamp concern you are probably good to return the truck to service. If the concern returns then I would replace the multifunction switch. Read on...

Also, forget about relays. Anything labeled "Stop Lamp Relay" is not for the lights. The relays are for the Caterpillar or Cummins ECM and simply isolate the modules from the lamp circuit and one other for the trailer tow brake light circuit.

The simple run down is Fuse F1-17 in the BJB (under the hood) supplies power directly to the brake pedal switch at the LG/RD wire. When the pedal is applied power is supplied into the multifunction switch at the LG wire and out from the multifunction switch on the LG/OG wire for the left rear and OG/LB wire for the right rear.

HTH


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Last edited by ford_doctor; 06-06-2018 at 07:57 PM.
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post #7 of 17 (permalink) Old 06-07-2018, 10:02 AM Thread Starter
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Hydraulic Brakes
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post #8 of 17 (permalink) Old 06-07-2018, 10:18 AM Thread Starter
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@Ford_Doc: We have already put a brand new MF Switch and still nothing. I checked the cable that runs to the brake light switch at the pedal for voltage and I'm getting 0 volts at all four connectors. I have a Green, Tan, and two stripped black wire on that cable. All the fuses at the junction box are good.
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post #9 of 17 (permalink) Old 06-07-2018, 10:21 AM
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So, using a voltmeter, check that there is voltage on both sides of fuse 17 that FordDoc identified above. If there is, then you've identified the segment with the issue. Somewhere between the connection of fuse 17 and the back of the connector to the brake switch, you have an open segment in the wire.

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I wonder if clouds ever look down on us and say, "Hey, look - that one is shaped like an idiot!"
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post #10 of 17 (permalink) Old 06-07-2018, 11:06 AM
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Okay this is silly, I attached the full Turn/Stop/Hazard schematic for you. Hope this helps.

FYI for the cost of the parts you already threw at this truck your company could have purchased a years subscription to the Motorcraft website with access to all the vehicle documentation available.


https://www.motorcraftservice.com/Home/Index
Attached Files
File Type: pdf 2002-F650-750-Brake-Lights.pdf (477.0 KB, 32 views)


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Last edited by ford_doctor; 06-07-2018 at 11:08 AM.
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post #11 of 17 (permalink) Old 06-07-2018, 11:19 AM Thread Starter
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I tested every single fuse, just for the hell of it and every single one had continuity on to both sides.
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post #12 of 17 (permalink) Old 06-07-2018, 12:12 PM Thread Starter
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Originally Posted by ford_doctor View Post
Okay this is silly, I attached the full Turn/Stop/Hazard schematic for you. Hope this helps.

FYI for the cost of the parts you already threw at this truck your company could have purchased a years subscription to the Motorcraft website with access to all the vehicle documentation available.


https://www.motorcraftservice.com/Home/Index
Brother, youre preaching to the choir... I've told my boss a million times... they just dont want to spend the money on stuff like that...lmao
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post #13 of 17 (permalink) Old 06-07-2018, 02:58 PM Thread Starter
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Originally Posted by ford_doctor View Post
Okay this is silly, I attached the full Turn/Stop/Hazard schematic for you. Hope this helps.

FYI for the cost of the parts you already threw at this truck your company could have purchased a years subscription to the Motorcraft website with access to all the vehicle documentation available.


https://www.motorcraftservice.com/Home/Index
I'm in talks with my Boss about getting access to the motorcraft website. Not sure how this will go but hopefully it will go well. @ford_doctor, thanks for the wiring diagrams, but I dont know if you noticed or not, but you sent me diagrams for a 2002 not a 2012. Thanks though.
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post #14 of 17 (permalink) Old 06-07-2018, 05:31 PM
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Could swear it read 2002... now the title reads 2012 and your now edited first post saus 2013. Which is it? I can get you the right diagram... jeese! I know my eyes are beginning to go but I know I read 2002 with my glasses on. LOL... no bother.


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post #15 of 17 (permalink) Old 06-08-2018, 09:11 AM Thread Starter
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See what happened was... I fat fingered it and put 2012 by accident, apparently I did it twice, but it 100% most definitely is a 2013 Ford F-750 With a Cummins... my bad.. lol Sorry bout that @ford_doctor
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