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Discussion Starter · #1 ·
Hi everyone,

Got a strange problem with the light in the boot (or trunk as Americans say). It never lights up.

Now here is what I have checked so far:
  • Bulb and assembly work fine. When I put 12v across the assembly the bulb lights up
  • 12v is present at the connector when the assembly is unplugged.
  • When the circuit is completed the light does not come on and there is only a minimal voltage drop across the bulb (0.4v).

All this indicates that there is a voltage drop somewhere else on the circuit, or in other words there is a high resistance somewhere else in the circuit.

Does anyone have any experience of this problem and can give a hint as to where the problem is? Hopefully it is on the earth side so I can just jump it to ground, but I thought I'd ask in case anyone has any tips?

Thanks in advance,
 

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Discussion Starter · #2 ·
Update on this: fortunately the issue is on the ground side so I can jump to ground on the chassis or perhaps the seatbelt assembly. Time to get the old soldering iron out.
 

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Update on this: fortunately the issue is on the ground side so I can jump to ground on the chassis or perhaps the seatbelt assembly. Time to get the old soldering iron out.
I seem to have this exact same problem currently (pun intended). Did your solution work for you? Where did you end up putting your ground wire?
 

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Discussion Starter · #4 ·
I seem to have this exact same problem currently (pun intended). Did your solution work for you? Where did you end up putting your ground wire?
Grounding the light is not a fix I have found out :)

Instead the light is actually supposed to be grounded through the latch mechanism and without that the trunk won't open. So instead you have to take off the panel on the trunk (absolute ball ache) and reterminate it there. I can post a circuit diagram later if you need. (y)
 

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Thanks for the reply! I popped the panel off and I'm trying to wrap my head around what I'm looking at and how that bulb runs to the latch. I think a circuit diagram would be very helpful.
 

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Discussion Starter · #6 ·
Thanks for the reply! I popped the panel off and I'm trying to wrap my head around what I'm looking at and how that bulb runs to the latch. I think a circuit diagram would be very helpful.
So W3 in the diagram below is the lamp in question. It actually grounds through the latch mechanism (V139). My model is the brown and black striped wire and not solid brown. So basically if you ground it somewhere else then the latch mechanism doesn't know that the door has been opened and won't unlock since it can see that current is flowing to the light still. So the problem is either that the latch mechanism is faulty or maybe just the wires need re-terminating.
Rectangle Slope Font Parallel Schematic
 

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So W3 in the diagram below is the lamp in question. It actually grounds through the latch mechanism (V139). My model is the brown and black striped wire and not solid brown. So basically if you ground it somewhere else then the latch mechanism doesn't know that the door has been opened and won't unlock since it can see that current is flowing to the light still. So the problem is either that the latch mechanism is faulty or maybe just the wires need re-terminating.
View attachment 9148
Thanks for the diagram. It's very helpful! I was able to deduce that the switch is the issue. In that diagram, the latch mechanism (V139) has 4 ports.

1 = computer
2 = trunk bulb ground
3 = ground
4 = power (I think)

So I disconnected the switch and jumped the ports directly and discovered some things. Jumping 1 to 3 activated the lights and the told the dash that the trunk was open. And jumping 2 to 3 turned my trunk light on!! So yep that pesky 2nd prong in the switch is faulty. I ordered a new one and it should be here soon.

But in getting the latch off my car I stripped the torx screws and am having a frustrating time finding a solution for removing the latch 🙄
 

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Discussion Starter · #8 ·
Good job buddy. I managed not to strip the torx screws but the pop off clips were another story. About half snapped.
 
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