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Hello New Friends, I just picked up a 2012 Lux TDI with the hopes of pulling some boats around. I'll get right to the story... I have an older trailer with incandescent lights and backed it into the lake with the trailer plugged in. Both bulbs shattered from being hot and hitting the cold water. I put new ones in and reminded myself not to do that again. Next day I unplugged the 4 way plug from my 7 pin adapter but didn't pull the whole adapter. I suspect it got dipped in the water when I backed the boat in. When I pulled the boat back out and plugged in the trailer I had nothing. No lights and no recognition from 'Reg a trailer was plugged in. Did some searching here and found some comments about fuses so checked those. #6 (15a) on passenger panel was blown but no others. (I have check everyone on both sides. ) Replaced that but still have no lights. There are 3v at plug and at light socket on trailer. Anyone have any idea what I'm missing? (While new to 'Reg I've taken a couple Jetta TDI's to 300k so generally do okay figuring stuff out but I'm stumped. Also, I don't have a vagcom either... ) Thanks in advance for any wisdom that may be bestowed!
 

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Are the lights you bought for the trailer compatible? If its older as you say, LED could cause an issue. Did you measure voltage between the pin harness and the outlet you plug the lights into on the trailer?
 

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Discussion Starter #3
The new bulbs are incandescent also. Voltage at 7 pin plug on 'reg is same as at light socket with bulb removed.
 

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Wow.. thats fascinating....................
 

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I always test the tow vehicle and trailer separately, having chased far too many red herrings on the trailer lighting front. I've made one trailer light test assembly with incandescent bulbs (it's actually the taillight assembly from a Scirocco) with enough wire to bring it up to the drivers seat of my tow vehicle that I plug into the 7-way at the back of the car. Most of the time, it ends up being a trailer wiring issue. I've made a set-up that clips to a car battery for testing from the 7-way plug to the trailer lights as well. You can buy theses test harnesses if you don't have time to make one. The test assemblies get around the problem of trailer light control modules that only send power when they sense a proper lighting load.

If your bulbs shattered when you backed into the water, you either had a damaged assembly or the wrong type of lamp for a boat trailer. Normally, they are sealed on the top and sides; they may be open on the bottom and operate on the bell-jar principle, with an air pocket inside. Sometimes they are completely sealed, which are better for trailers that operate in road salt conditions.
 

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@buckwheat I think you are on to something. I haven't gotten a chance to go through your whole process but I did try a different vehicle on the boat trailer and while the running lights turn on I have no brakes or turn signals which is the exact same bulb and is clearly working. I'll give your idea a systematic assessment a try and update here for the benefit of others! Thank you for your engagement and help!
 
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