Weird tail light issues

[Jaytayfofo]

Hey everybody. New to the class . Just bought a 2015 GT and on the way home, with my wife following me, she called me and told me the brake lights were not working. We pulled over and checked it out. Come to find out, the brake lights, blinkers, and hazards are not functioning. The top brake light is working fine and the running lights are working fine. I have checked all the fuses, but I’m not an electrical expert by any means. Has anybody else had anything similar? Also when I lock/unlock the car sometimes the rear lights don’t illuminate at the same time. Drivers side will come on first, followed by the passenger side. Opposite when they go off. Sometimes the passenger side will go off first. I have a video that I will try to attach. Pretty stressful not being able to drive a car you just spent a lot of money on. Thanks.

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[Falk03]

All these functions are controlled by the BCMB (Body control module B) which is located in the trunk on the right hand side behind the subwoofer. Fuse 36 in the BCM in the footwell area would be responsible for this.
If the fuse is alright, the best thing would be to check for error codes.

Any chance the previous owner could support you? It is always an option to go to the dealer or maybe you got a friend with an OBD adapter and FORScan. Having the error codes would definitely help.

 

[Jaytayfofo]

All these functions are controlled by the BCMB (Body control module B) which is located in the trunk on the right hand side behind the subwoofer. Fuse 36 in the BCM in the footwell area would be responsible for this.
If the fuse is alright, the best thing would be to check for error codes.

Any chance the previous owner could support you? It is always an option to go to the dealer or maybe you got a friend with an OBD adapter and FORScan. Having the error codes would definitely help.

Unfortunately the previous owner is claiming to have not been aware of the issue. Do you think I could pull the codes with my N gauge?

 

[Elp_jc]

So turn-signals work? That'd rule out the tails themselves, AND the brake switch 'pad'. If they don't work, I'd immediately check your brake switch, and make sure the yellowish pad it's supposed to be touching is still there. If previous owner didn't change it, it probably cracked, and fell off by now (very common issue on older cars), and that might have burned the brake/turn-signal lights. I replaced all 3 pads on my new Bullitt, to avoid forgetting about them... although I think that triggers limp mode, so it might not be it. But replace them anyway, since it's only a matter of time now. I bought mine from a Toyota dealership, but I think Advanced Auto or one of those sell them (look for a thread on that).

Having said that, the flashing issue indicates a BCM module issue, so that's probably the issue. Finally, I'd get FORScan now, so you can check things like that quickly, and make other 'comfort' changes you want. Good luck.

 

[Jaytayfofo]

So turn-signals work? That'd rule out the tails themselves, AND the brake switch 'pad'. If they don't work, I'd immediately check your brake switch, and make sure the yellowish pad it's supposed to be touching is still there. If previous owner didn't change it, it probably cracked, and fell off by now (very common issue on older cars), and that might have burned the brake/turn-signal lights. I replaced all 3 pads on my new Bullitt, to avoid forgetting about them... although I think that triggers limp mode, so it might not be it. But replace them anyway, since it's only a matter of time now. I bought mine from a Toyota dealership, but I think Advanced Auto or one of those sell them (look for a thread on that).

Having said that, the flashing issue indicates a BCM module issue, so that's probably the issue. Finally, I'd get FORScan now, so you can check things like that quickly, and make other 'comfort' changes you want. Good luck.

No, the turn signals are not working. Could that mean the tails even though running lights work fine? Everything I read/hear ends up mentioning the BCMB. I guess that’s where I should start.

 

[WD Pro]

Could it be that they have (or have had) sequencers in there that have either gone bad (or the plugs have been damaged removing them) ?

Hope you get it sorted

WD

 

[Jaytayfofo]

Could it be that they have (or have had) sequencers in there that have either gone bad (or the plugs have been damaged removing them) ?

Hope you get it sorted

WD

That’s very possible. Is there a way I can tell?

 

[WD Pro]

The sequencers I have (bear in mind I’m on a euro model) fit inline between the loom plug and the lamp unit plug.

e.g. https://store.exoticponymods.com/pr...ustang-tail-light-sequencers-ultimate-version

Maybe pull some trunk trim out and inspect that connection - particularly the internal pins once the connection is separated ? (even if no sequencers are present)

WD

 

[Rapid Red]

" brake lights, turn signals, and hazards are not functioning"

Rear only ?
Tail lights work?

 

[Elp_jc]

No, the turn signals are not working. Could that mean the tails even though running lights work fine? Everything I read/hear ends up mentioning the BCMB. I guess that’s where I should start.

You didn't mention what the front lights are doing, but I agree everything points to the BCM-B. But still check the brake switch pad I told you about, because it must be cracked on a 2015 by now, and about to fall into pieces on the floor mat at any time, triggering limp mode, which limits speed to 20 mph or so. And with the brake lights constantly on. Good luck.

 

[wazslow]

You didn't mention what the front lights are doing, but I agree everything points to the BCM-B. But still check the brake switch pad I told you about, because it must be cracked on a 2015 by now, and about to fall into pieces on the floor mat at any time, triggering limp mode, which limits speed to 20 mph or so. And with the brake lights constantly on. Good luck.

The OP said the third brake light is working, so I don't think it's the brake light switch.

 

[Falk03]

If the third brake light is working, it is not the brake light switch. If the running light is working, I would assume the tail light is ok, because it is the same LEDs and electronics controlling this.
The hint with the bent terminals because of a tail light sequencer is a very good one, but why on both sides and why are the running lights still working? Or maybe there are still tail light sequencers and they went bad. Then removing the sequencers should solve the issue.

Without working turn signals, you should have hyperflash. Or somebody changed the BCM configuration. A new BCMB shouldn't be expensive, but I would only swap it after confirming it actually is the BCMB. I habe a BCMB lying around, but it does not make sense to send it to the US from Germany.
Nevertheless first thing should be checking the connectors and then for any error codes (DTCs). Not sure if the NGauge can do that. The software (FORScan) is actually for free, but you would need an OBD connector (starting around $15).

 

[Elp_jc]

The OP said the third brake light is working, so I don't think it's the brake light switch.

You're absolutely correct. I missed that. Sorry.

Having said that, I suggested to him to check the switch pads, before they fail, leaving him stranded.

 

[Cobra Jet]

Most likely bad BCM module.

Post 25 of this thread may be helpful for diagnosis as well as other responses in that thread:
https://www.mustang6g.com/forums/threads/tail-light-out-then-back-on.101551/page-2

 

[Jaytayfofo]

" brake lights, turn signals, and hazards are not functioning"

Rear only ?
Tail lights work?

Yes. Read only. Headlamps and front turn signals function as they should.

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