Tail light not working ???

[RejoiceWay]

Passenger side stop tail light not working. Have voltage back to connectors by refrigerator. Contacts of signal and lamp have been cleaned. Light bulb is confirmed good. Thinking the wiring is broken and grounded so a short circuit (when connector at refidgerator location is “plugged in”, car (2017 Touareg) reduces voltage to zero to right tail light. Any idea how to access wiring in back section of TM to check for potential problems would be helpful..

[Bill]

Passenger side stop tail light not working.

Which one does not work? Stop (brake) light? Tail (running) light? Both?

Terminology: If you had a short circuit, it would blow a fuse, and a blown fuse would disable other lights as well. Since you have neither symptom, most likely there is an open circuit, not a short. "Open circuit" means that current is available and ready to flow, but it can't flow because the wire is broken or disconnected, or "open". So we need to look for that "open". Most likely it is within the light fixture.

First step - take the red plastic lens off the fixture. Within the fixture, there should be a short wire connecting the shell of the bulb socket to ground, usually one of the fixture's mounting screws. This is the ground wire for the fixture. Is this wire present and firmly connected at both ends? With the TV connected to the TM, engine running, the running lights turned on, and the brakes applied, wiggle it. Any response?

There should also be two wires coming out through the base of the fixture, both going into the base of the socket. Wiggle them. Any response?

Assuming no responses, do you have a test meter of some kind (voltmeter, etc) kind? If so, remove the bulb from the socket, and confirm that there is voltage between the center contact of the socket and ground. Be careful probing around inside the socket. There is 12 volts in there. It won't hurt you, but sparks can surprise you and perhaps blow a fuse in the tow vehicle.

If you have voltage there, then the problem has to be on the ground side, and that is the most common.

Get back to us with these results so far.

Bill

[RejoiceWay]

hello Bill. Lots of good info. So yes, the running light works at the right taillight assembly but the brake light/turn signal does not. There is no voltage to the pin for the brake light. The ground is functional.

I do not know for sure how the electrical protection system works on the Touareg. At a butt connector for the turn signal about halfway back on the trailer, if I pull apart the connector there is voltage on the line side of the connector. Once the load side is plugged into the connector, the voltage for the right stop wiring goes to zero. The left side directional still functions. I suspect that VW has an isolation system to avoid impacting the car’s taillights. If I turn off the car, disconnect the butt connector and turn on the right directional, the 12 volt pulsating voltage returns.

Other posts suggest that I look for a pinched wire due to the “folding” process utilized on Trailmanors. I looked carefully at the specially wrapped wire bundle on the outside of the trailer for any imperfections such as pinched wires. None were evident, so am thinking of scrapping off a small section of insulation on the brown brake wire followed by a continuity test back to the load side butt connector. Will do this to confirm the brown wire is operational on the outside of the trailer. (Will wrap scrapped wire wirh electrical tape and later liquid tape to properly insulate it). If the exterior wire is good, then it’s time to start cussing as the problem is in the wall of the trailer.

Other alternatives for identifying the damaged wire would be most welcome.

[Bill]

Well OK! I did a quick internet search on "Toureg tail light short circuit protection", and it seems many people have had weird problems similar to yours. The Germans do interesting things, and if they have put in some kind of short circuit protection in the light circuits, then I am out of my depth, and will have to withdraw much of my post.

You may find a physical wiring diagram helpful - where do the wires in the TM actually run?

Do you have what we used to call the blue book or blue binder? If so, there is a diagram of the physical routing of the wires and connections in the TM roof. If you don't have the manual, you can download it from the TM Technical Library, at
https://www.trailmanorowners.com/for...ad.php?t=13839
The various manuals are all very similar, so choose the Classic manual. Go to Page 42 to see the rear roof diagram.

You can see that the wiring goes from the refrig area, forward to the shell edge, up the driver's side to the roof, then inside the edge of the roof and back to the rear wall. At that point the wires divide and go to their individual destinations - in your case, the passenger side tail light assembly.

Since power is good as far as the refrig, the fault can be in the bundle that rises outside the trailer, as you suggested. Or the fault may be in the tail light assembly itself. I think it unlikely that the fault is elsewhere. In my opinion and experience, it may be easier to start looking in the lamp fixture, and break into the riser wires only if that doesn't work. Your choice.

In the absence of Germain engineering, the most common place for faults is in the light fixture. The fixture is easy to remove for inspection and testing, and easy to replace (with new caulk) when you are done. With the fixture off the wall, it is common to find that the ground to the trailer skin has become interrupted in some way. Ground is done with a wire from the shell of the bulb socket, either to one of the fixture's mounting screws, or through the base of the fixture and into a connector inside the TM wall near it. Look carefully.

The good news is that you don't have to break into the wires inside the rear roof.

Let us know what you find.

Bill

[RejoiceWay]

Hello Bill--Thanks again for staying with me on this. Well, I did check all the connections at the taillight and they were good including the grounding. I needed to get back on the road, so I installed a wire from the load side of the brown butt connector at the refer area thru the interior of the Trailmanor and out the back window to the right taillight. At the taillight, I disconnected the brown wire and isolated it. I then connected the new wire to the brake lamp. It worked fine. Back home, I used a better-quality meter (Fluke 117) and checked the resistance. The ohms on the new wire were almost identical to the ohms on the old brown wire. I then opened the end of the brown wire at the taillight and check the resistance from the load side brown wire to ground (8 ohms) which was nearly identical to the earlier test. So this confirmed that the brown wire is not broken but is grounded which makes it a bugger to locate the problem area. Do you have any recommendations as to removing the trim pieces inside the TM shell so I can inspect the wiring? As always, thank you for your time and input.