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Discussion Starter #1
I have a 2004 Passat that has the parking lights and tail lights staying on after the car is shut off. It will run the battery dead, so I have to disconnect the battery when I'm done driving it. I suspected moisture under the driver's side carpeting and it was definitely wet. I got everything dried out and then inspected the CCM module. The module looked fine along with the electrical connectors (no corrosion) and all the components that the CCM controls are working fine. I have the headlight switch disconnected and still the parking and tail lights are staying on after the car is shut off. Also, the back up lights are not working.

What would be powering up the parking and tail lights and causing the back up lights not to work? Thanks in advance!
 

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All I can say is..... good luck! :)

Obviously, something is back-feeding power into the side lights circuits (which are two independent circuits - left separate from right) - and, it's an 'always-live' circuit. There's no 'control unit' to go after - the headlight switch is fully responsible for lights on these cars.

Any wiring funkiness (read: 'modifications') in the car? Trailer electrical?

Reverse lights: That depends on if you have an automatic or manual transmission (very different controls between those two.)
 

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Discussion Starter #3
Thanks---that did clear up one question I had---that it did not have a control unit. For what it's worth regarding the back up lights, it does have an automatic transmission.
 

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A couple of thoughts:

First, closely inspect the headlight switch connector for melting/overheating/broken wire strands, etc.

Second, if nothing is obvious there, the parking light contact from the headlight switch (14/58R, green/red wire) feeds three fuses:
> fuse 4, license plate lights, gray/yellow wire
> fuse 22, right parking lights, gray/red wire
> fuse 23, left parking lights, gray/black wire

I'd pull those three fuses individually to see if the unwanted power is coming from the green/red wire, upstream of the fuses, or from downstream of one of the three fuses.
> If the fault is somewhere on the green/red wire or headlight switch connector, pulling the fuse will turn off only the lights that fuse serves.
> If the fault is on one of the three circuits, pulling the fuse will turn off all the other lights, but not those on that fuse.

That should significantly narrow down where you need to look. (Ref. Bentley schematic 48)
 

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Discussion Starter #7
Thanks for that info on the fuses---that will be extremely helpful. I checked the connector/wiring for the headlight switch and nothing was burnt up there (however, good call on diagnosing!) It will be next week before I will be able to get back to this project for checking on the fuses.

I did open up the carpeting on the passenger side to find it was pretty wet also. I inspected the wiring harness and the transmission ECU but did not see any moisture related corrosion on the harness nor the connector for the ECU. I will be opening up the carpeting in the back also to see if there is any moisture related wiring issues.
 

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Discussion Starter #8
Found the problem! I lifted the carpeting behind the driver's seat and found that the insulation under the carpet was saturated with moisture. Under the wet insulation, I seen the wiring harness was a corroded mess. I removed the tape around the harness and got in there and separated the wiring and ended up cutting and splicing in seven different wires---everything is back in working condition now! Currently drying the insulation and clearing out the sunroof and under hood plenum drains. IMG_1186.jpg Thanks to all that replied!
 
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