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    VWVortex


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    Thread: trunk light out

    1. Member
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      12-02-2010 08:30 PM #1
      I've been trying to fix this seemingly simple light, but WTF!

      Bulb is not blown, checked with 12V battery.

      No fuses are blown.

      All wiring is intact.

      VAG-CUM Shows absolutely zero errors.

      Anyone else have this issue? Any ideas?


      2007 Jetta Wolf 42k miles. Hasn't worked since I got the car bone stock.
      2007 Jetta Wolfsburg. CAI w/ 9" filter. Drilled and slotted 13" brakes. Interior footwell neons. Kicker zx1000.1 amp. 1000wrms 15" Kicker L7 w/ 5 cu. ft. ported box. 55watt 5000K HID lows, highs, driving lights and fogs. 2nd battery in trunk. White marker lights, clear lens. Quad blind spot mirrors. Hard wired radar detector. All interior LEDs.

    2. Junior Member
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      12-03-2010 01:25 AM #2
      I would start with a continuity tester or a multimeter if you have either one laying around. Test the pins on the connector's end and go from there.

    3. Member
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      12-04-2010 04:28 PM #3
      Well, I checked the wires running from the trunk light to the computer and the resistance is the same along them at the trunk and at the computer so I think the wires are fine. I think it's something with the computer and I don't know where to start.
      2007 Jetta Wolfsburg. CAI w/ 9" filter. Drilled and slotted 13" brakes. Interior footwell neons. Kicker zx1000.1 amp. 1000wrms 15" Kicker L7 w/ 5 cu. ft. ported box. 55watt 5000K HID lows, highs, driving lights and fogs. 2nd battery in trunk. White marker lights, clear lens. Quad blind spot mirrors. Hard wired radar detector. All interior LEDs.

    4. Member JetTurbo's Avatar
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      12-04-2010 05:41 PM #4
      Quote Originally Posted by feelinjunky View Post
      Well, I checked the wires running from the trunk light to the computer and the resistance is the same along them at the trunk and at the computer so I think the wires are fine. I think it's something with the computer and I don't know where to start.
      Are all your interior lights dead?

      The trunk light receives its 12V power from the same source as all ceiling lights and glove box light.
      (Footwells are separate, but the rest of the interior lighting shares one circuit.)
      This 12V power is normally not switched and should be available even when the light is off.
      (The 12V does switch off after the car is off and idle for 20 minutes or so,
      but all interior lighting will go with it.)

      Most likely your issues lies in the trunk latch.
      The trunk latch switches the ground side of the trunk light to turn it on / off.
      The same switched ground is connected to the Comfort System Central Control Module J393
      for monitoring trunk open / closed for the MFD.

      Does your MFD register trunk open?
      2102 Golf R, 2008 US b6 Passat 4-motion - sold 2006 US Mk V bmp GTI mt (230,000 miles/ 7 yrs)

    5. Member
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      12-05-2010 07:17 AM #5
      Yes, I checked all the obvious.

      It says the trunk is open on the dash when the trunk is opened, so the switch shouldn't be fried.

      All interior lighting works as it should.

      I'm gonna try replacing the housing for the trunk light itself with a straight pull from a newer Jetta. Idk what else could be wrong.

      Thanks for your help man.

      Edit: also, my 12V power goes off when the car is off. The key has to be in the "on" position for it to work. But the trunk light doesn't work when the car is off, on, or ever.
      Last edited by feelinjunky; 12-05-2010 at 07:21 AM.
      2007 Jetta Wolfsburg. CAI w/ 9" filter. Drilled and slotted 13" brakes. Interior footwell neons. Kicker zx1000.1 amp. 1000wrms 15" Kicker L7 w/ 5 cu. ft. ported box. 55watt 5000K HID lows, highs, driving lights and fogs. 2nd battery in trunk. White marker lights, clear lens. Quad blind spot mirrors. Hard wired radar detector. All interior LEDs.

    6. Member JetTurbo's Avatar
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      12-05-2010 11:50 AM #6
      Quote Originally Posted by feelinjunky View Post
      ... I'm gonna try replacing the housing for the trunk light itself with a straight pull from a newer Jetta. Idk what else could be wrong. ...
      There are no moving parts in the fxiture, you would think any damage would be obvious.
      Stranger things have happened I guess :iono:

      mk5 trunk light fixture with aftermarket bulb



      If you have access to meter, test for DC voltage,
      There should be constant 12V DC between the trunk light connector's hot pin and vehicle ground,
      independent of the switch.

      The trunk light is switched through the ground side of the connection.
      You can check the ground side switch with a continuity check between
      the trunk light connector's ground pin and vehicle ground.
      It should show a compete circuit with the trunk open,
      and an open circuit when the trunk is closed.

      If you need the wire color / codes for 12V DC and ground, I'll get them when I return from the Saints / Bengals massacre.

      Quote Originally Posted by feelinjunky View Post
      Edit: also, my 12V power goes off when the car is off. The key has to be in the "on" position for it to work. But the trunk light doesn't work when the car is off, on, or ever.
      "The key has to be in the "on" position for it to work."
      If you are talking about the accessory power outlet, its unrelated.
      When I refer to 12V I am referring to the current in a circuit, not the accessory power outlet.
      The 12V in the trunk light circuit is constant on with key on or off.
      It only disables after the key off inactivity timeout (≈20 min).
      2102 Golf R, 2008 US b6 Passat 4-motion - sold 2006 US Mk V bmp GTI mt (230,000 miles/ 7 yrs)

    7. Member
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      12-05-2010 12:27 PM #7
      Quote Originally Posted by JetTurbo View Post
      "The key has to be in the "on" position for it to work."
      If you are talking about the accessory power outlet, its unrelated.
      When I refer to 12V I am referring to the current in a circuit, not the accessory power outlet.
      The 12V in the trunk light circuit is constant on with key on or off.
      It only disables after the key off inactivity timeout (≈20 min).
      Yes, I was referring to the power outlet. Sorry, now we're on the same page.

      Ok, I'll check the +12V wire from the light with vehicle ground and see if I'm getting power. Then I'll check the ground cable from the trunk light with veh. ground with the trunk open and see if I'm getting continuity on the circuit. Then I'll have to crawl in the trunk with it closed and check the same for discontinuity. Thanks.

      My reasoning behind replacing the housing is that it looks corroded on the connection end where the bulb makes contact with the metal. I would clean it, but it's less effort for me to replace it (and free - local "junk"yard has a 2010 Jetta).

      I'll post my results here and see where I'm at.


      EDIT: By the way, when you say no moving parts, umm, it's moving quite a bit. I have a 2000w ported sub and amp in the trunk that sometimes run at max volume. But this is irrelevant as the light didn't work before I put in my sub.
      Last edited by feelinjunky; 12-05-2010 at 12:34 PM.
      2007 Jetta Wolfsburg. CAI w/ 9" filter. Drilled and slotted 13" brakes. Interior footwell neons. Kicker zx1000.1 amp. 1000wrms 15" Kicker L7 w/ 5 cu. ft. ported box. 55watt 5000K HID lows, highs, driving lights and fogs. 2nd battery in trunk. White marker lights, clear lens. Quad blind spot mirrors. Hard wired radar detector. All interior LEDs.

    8. Member
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      12-05-2010 04:03 PM #8
      Ok, found the problem. BIG thanks to you for posting the pic of the light housing.

      I noticed you have a diode in series into those fork-like connectors.

      I did not have a diode there. There was nothing there and therefore the circuit wasn't complete.

      I just put in some bare wire because I see ZERO function for a diode there...

      Now, for the first time, I have a trunk light! Thanks a lot for your help man. It's really weird that I didn't have that part there though.
      2007 Jetta Wolfsburg. CAI w/ 9" filter. Drilled and slotted 13" brakes. Interior footwell neons. Kicker zx1000.1 amp. 1000wrms 15" Kicker L7 w/ 5 cu. ft. ported box. 55watt 5000K HID lows, highs, driving lights and fogs. 2nd battery in trunk. White marker lights, clear lens. Quad blind spot mirrors. Hard wired radar detector. All interior LEDs.

    9. Member JetTurbo's Avatar
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      12-05-2010 04:39 PM #9
      Quote Originally Posted by feelinjunky View Post
      Ok, found the problem. BIG thanks to you for posting the pic of the light housing.

      I noticed you have a diode in series into those fork-like connectors.

      I did not have a diode there. There was nothing there and therefore the circuit wasn't complete.

      I just put in some bare wire because I see ZERO function for a diode there...

      Now, for the first time, I have a trunk light! Thanks a lot for your help man. It's really weird that I didn't have that part there though.
      Bengals sucked like always. Gave it away today.

      Glad to hear its working.
      Maybe those vibrations you referred to knocked the part out?
      2102 Golf R, 2008 US b6 Passat 4-motion - sold 2006 US Mk V bmp GTI mt (230,000 miles/ 7 yrs)

    10. 02-06-2011 04:05 PM #10
      Thanks to this thread our trunk light is working now too! We bought an 08 Jetta a few weeks ago from the local VW dealership, and while I have the VW certified pre-owned warranty, this seemed like a dumb thing to have the dealership investigate. Turned out the diode had disconnected on one side, barely hanging on on the otherside. Thanks!

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