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2015 Mustang GT Taillight Sequential Issue

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2015 Mustang GT Taillight Sequential Issue

Old 09-14-2018, 10:37 AM
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Default 2015 Mustang GT Taillight Sequential Issue

I have a 2015 mustang gt that has recently started having issues with the tail light sequential on the passenger side not lighting up on the bright setting (for brake and turn signal) but will operate the dim setting when the lights are on. It is not occurring all the time, I can have the car sitting in the garage and have it not working, go down the street and have it working again, then go to another store and have it out again.
Any ideas what could be causing this? Recommendations or links associated. Pictures attached.

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Old 09-14-2018, 02:57 PM
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Bulb on its way out or a bad bulb socket. When it doesn't blink, all the way over does the turn signal blink faster on the dash? If does, then it's one of the thing I mentioned, if not, no idea.
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Old 09-14-2018, 03:12 PM
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Yes, it blinks as if I light is out, however these are led boards instead of normal bulbs and all of that is internal (unserviceable). I'm wondering if there is a wiring issue somewhere or something.
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Old 09-14-2018, 04:33 PM
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So you have a harness addition for the sequentials, or is it built into the assembly?

If it is built into the assembly, well, you're in need of a new assembly...

If it is a harness, remove the harness, back to factory, see if the light will
bright when it is supposed to, if not, you lost that portion of the circuit
for the LED panel in that lens. The difference between LO and HI on LEDs
is voltage application to the same LED panel. The parking lights, a resister
between the car parking +12 power lead and panel is used to LO light the panel.
Brake or Signal, the full 12V is applied from the car side wire to brighten the

So, either the car side Brake/Signal wire has a bad connection, or it terminates
at the LED panel, and does not get through because a diode or current limiting
resister on LED panel board has failed.

Something like this:

So, as you see, the Parking light power is reduced by the Resister so that panel is LO.
When Brake/Parking is applied, no resister for full brightness.

The diodes keep current from going back through, so when the brake/signal is
on, power is not fed back through the parking. With Parking on, no flow
back through the Brake/Signal.

IF the HI diode failed, you get no HI lighting. Some use the litle
fuses you can't replace after the diode... IF that goes, no HI either.

CRUDE diagram, I was not going to design the whole panel....

Last edited by 08'MustangDude; 09-14-2018 at 04:38 PM.
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Old 09-14-2018, 04:34 PM
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Uhh i remember issues with pinched wires in the trunk, but don't remember the details.
Search on here or online.
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Old 09-14-2018, 04:41 PM
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It is the stock harness, though referring to the comment about pinched wires, I recall reading that as being an issue with the backup camera (which is also intermittently going black or sliding the image up and down periodically) but I could not find where these pinched wires they were referring to were ere located. Think this may go hand in hand?
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Old 10-03-2018, 01:07 PM
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Had a similar issue with my 2015. After doing some research on a lot of Mustang forums I found that this can be a battery issue. My car was not driven much in the winter which resulted in the battery getting just low enough to cause this problem. Ford has noted this as well and I even read where there were possible upgrades in software to address this. Keeping my battery fully charged eliminated the issue for me. Hope this helps.
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