2005 STS tail light
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Cadillac STS Forum - 2005 through 2012 Discussion, 2005 STS tail light in Past Cadillac Vehicle Discussion; My 2005 STS has a drivers side tail light out. Can I replace a bulb myself, or do I need ...
  1. #1
    Jamerock is offline Cadillac Owners Member
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    2005 STS tail light

    My 2005 STS has a drivers side tail light out. Can I replace a bulb myself, or do I need an entire LED? Should I take it to the dealer?

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    ddalder's Avatar
    ddalder is offline Cadillac Owners Connoisseur
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    Re: 2005 STS tail light

    These are easy to change, but they are not a serviceable item so you'll need to purchase the entire tail lamp. I'd have to check the schematic, but there is a chance left and right may be fused separately. Checking this would be a better place to start, then go the expensive route only if necessary.

    I'm assuming it's the whole lamp that's out, not just some individual LED's?

  4. #3
    Jamerock is offline Cadillac Owners Member
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    Re: 2005 STS tail light

    That's correct. It's the whole lamp.

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    ddalder's Avatar
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    Re: 2005 STS tail light

    The park lamps are fused separately, left and right, in the underhood fuse block. The stop lamps are fused in the right rear fuse block but both left and right are on the same circuit. If absolutely nothing works (brake, signal, park) then you have either a bad tail lamp assembly or bad wiring. My next step would be to pull the connector off the tail lamp and check voltages.

    Cavity 'D' is ground and will be a black wire.
    Cavity 'A' is the park lamp supply voltage and will be a purple wire.
    Cavity 'E' is the brake lamp supply voltage and will be a light blue wire.

    If you look very closely at the connector, you should see the cavity letters embossed in the housing. This will help you to identify the cavities.

    With the park lamps on, you should have roughly 12 volts when measuring across cavities 'D' and 'A' (with the engine off). When someone steps on the brakes (car must be running), you should see about 13-14 volts when measuring across cavities 'D' and 'E'. If you have proper voltages, your tail lamp assembly is defective and needs to be replaced. If you don't, you have a wiring problem that will need to be investigated.

  6. #5
    Jamerock is offline Cadillac Owners Member
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    Re: 2005 STS tail light

    It's just the brake light. The signal and park lights work.

  7. #6
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    Re: 2005 STS tail light

    short in the board, youll need a new lamp

  8. #7
    Cadjiek is offline Cadillac Owners Fanatic
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    Re: 2005 STS tail light

    Do they still use a switch at the brake pedal? Could that be the problem? I don't know if he got a good reading from cavity E or not.

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    ddalder's Avatar
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    Re: 2005 STS tail light

    Quote Originally Posted by 1BadCadSTS View Post
    short in the board, youll need a new lamp
    It is unlikely to be a short or it would have blown a fuse and neither side would work. If there is a problem with the tail lamp, it is most likely an open circuit due to corrosion from moisture intrusion. It's also possible there is a problem with the logic in the lamp.

    Quote Originally Posted by Cadjiek View Post
    Do they still use a switch at the brake pedal? Could that be the problem? I don't know if he got a good reading from cavity E or not.
    Yes, there is still a brake lamp switch. Since one side works, this rules out the fuse, switch and relay (located in the right rear fuse block).

    If there is any question about the supply voltage to the connector, I would double check it again. The likelyhood of wiring is small because the wire runs directly from the rear fuse block to the connector and does not pass through any other connectors. Also, none of the wiring is exposed to the exterior of the car.

    I guess what I'm saying is "correct" troubleshooting technique dictates checking all wiring up to the lamp assembly prior to replacement. The tail lamp is quite likely the problem but also expensive. Rule out all other causes before spending money on costly parts.

  10. #9
    1BadCadSTS's Avatar
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    Inside the lamp is a circuit board that is shot

  11. #10
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    Re: 2005 STS tail light

    Anyone have the P/N for the tail lights? I have a similar phenomenon... brake light is out, but turn signal and tail light still works.

  12. #11
    Subsailor613's Avatar
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    Re: 2005 STS tail light

    Aren't we forgetting something, the brake lights signals,come through the multi-Function switch,
    to cut out the brake signal, and blink the appropriate, tail light ?
    I am NOT saying ,the Whole light is good or bad,
    the voltage readings "NEED" to be read at the connector as:
    ddalder suggests above !
    Good Luck.

  13. #12
    bbshriver's Avatar
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    Re: 2005 STS tail light

    I can check that easily enough, but I'd like to have a p/n since it seems like the tail light is the most likely culprit.

    If the brake light signal is the same as the blinker signal then how would one work and not the other, on only one side?

  14. #13
    Subsailor613's Avatar
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    Re: 2005 STS tail light

    When you put your right blinker ON, do both tailights blink ?
    OR only the right One,The multi-Function switch seperates
    that function.

  15. #14
    bbshriver's Avatar
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    Re: 2005 STS tail light

    Both turn signals work as they should, both tail lights work as they should, and the left side and center brake lights work as they should. It is only the right side brake light that is not functioning.

    Also I have noticed on the right side tail light one of the individual LED's is intermittent.. sometimes it's on sometimes it's off.

  16. #15
    moests is offline Cadillac Owners Member
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    Re: 2005 STS tail light

    my driver side brake light is out all other lights work

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