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BCM?

Tiny
CELLJUNKIE02
  • MEMBER
  • 2006 MAZDA 6
  • 2.3L
  • 4 CYL
  • TURBO
  • 4WD
  • MANUAL
  • 171,217 MILES
I plugged in my plate lights after swapping out my trunk keeping my same harness. About thirty seconds after that every light on the dash came on and the car horn started constantly going off. While I was driving burnt electrical smell very strong and could see smoke coming from the interior fuse box. The only way it would stop was disconnecting the battery. Is this the BCM Help?
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Monday, March 4th, 2019 AT 9:49 AM

11 Replies

Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
  • 42,882 POSTS
Hello,

It sounds like you have the wrong harness or connected in incorrectly. Can I ask if all lights are working if all are working can you tell me if anything has stopped working? Please let me know.
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Tuesday, March 5th, 2019 AT 11:09 AM
Tiny
CELLJUNKIE02
  • MEMBER
  • 8 POSTS
The tail lights and reverse lights were working fine, drove for thirty miles. It was when I plugged in my plate-lights that the dashboard warning lights all started flickering, the horn started going off and the normal burnt electrical smell but I could see smoke so I pulled it over and pulled the battery. Waited a few minutes and disconnected the trunks harness
touched the battery to the terminal with the car off and the horn started up again it's like it's stuck on. I'm worried I fried something bad enough where I soldered some of the wiring together and I'm thinking withing harness or new fuse panel/ box. I haven't tried giving it power again as I wanted to try and diagnose this w someone first hoping if they might have an idea what it is. Which I think it was plugged in incorrectly as I wasn't the only one working on the harness. Any thoughts?
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Wednesday, March 6th, 2019 AT 3:06 AM
Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
  • 42,882 POSTS
Did you install LED light bulbs by chance? Those can cause issues. Here is the wiring diagrams for the running lights which run the license plate light so you can see how the system works. It sounds like you may have burned up the BCM I would try a used/rebuilt unit to see what happens after you check the wiring using this guide.

https://www.2carpros.com/articles/how-to-check-wiring

Check out the diagrams (below). Please let us know what you find. We are interested to see what it is.
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Wednesday, March 6th, 2019 AT 2:50 PM
Tiny
CELLJUNKIE02
  • MEMBER
  • 8 POSTS
Yes, I do have the LED lights. But never any issues before. However, the trunk they were in before was carbon fiber. This isn't. And I took pictures of the wiring of the LED brake and reverse lights to make sure. And those were working after I swapped the trunk for miles. But Mazda had suggested that the interior fuse boxes on these cars have a computer and sounds like I need to replace that. I'm just having issues getting the interior fuse box out and haven't had much luck on YouTube for this specific 2006 Mazdaspeed 6.
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Thursday, March 7th, 2019 AT 3:18 AM
Tiny
CELLJUNKIE02
  • MEMBER
  • 8 POSTS
The PCM or BCM I can't remember what they said.
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Thursday, March 7th, 2019 AT 3:19 AM
Tiny
CELLJUNKIE02
  • MEMBER
  • 8 POSTS
Now I'm almost positive it's the BCM as dozens of forum sites have had exact same symptoms and have replaced the BCM. Also that is the only source of the smell coming right from that box. All fuses are good none are blown.
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Thursday, March 7th, 2019 AT 6:12 AM
Tiny
KEN L
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Yep its sounds like the BCM is out. But we better figure out why before you plug a new one in. Did the carbon fiber lid have a ground strap or? What was the difference?
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Thursday, March 7th, 2019 AT 9:44 AM
Tiny
CELLJUNKIE02
  • MEMBER
  • 8 POSTS
No, no grounding except what was in the harness. It's carbon fiber outside and inside was fiberglass. No metal except the bolting. And I found the issue. The not very smart guy who wired the right half of the harness as I was wiring the left half, plugged the harness together with what seems like power to power. Plugged it into itself. Sounds like it back fed right into the BCM. And the burnt electrical smell is coming directly from the BCM. Not from under the hood or the trunk just there. Other problem is I need to figure out if I can drive my car after I put the new BCM in so I can get to the desk to get it flashed to my key code. Or can I just plug it in and be good with it? Doubtful it's never that easy, lol but worth a question.
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Thursday, March 7th, 2019 AT 9:49 AM
Tiny
CELLJUNKIE02
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  • 8 POSTS
Yup, BCM is toast.
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Friday, March 8th, 2019 AT 4:12 PM
Tiny
CELLJUNKIE02
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Thanks for all the help man. I appreciate it. I'm ordering one with the same model number same year make and model as mine for $65.00.
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Friday, March 8th, 2019 AT 4:13 PM
Tiny
KEN L
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Nice work, let me know when you get it installed, sounds like you got the wiring figured out. I would double check everything before plugging the replacement BCM in.
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Saturday, March 9th, 2019 AT 12:20 PM

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