Electrical mystery problem... HELP!

[caseydog]

I just got a new tow vehicle, and added a hitch and plug-n-play wiring harness. I had a shop foreman at a Porsche repair shop help me install the hitch and wiring.

I took the TD out for its first journey, and everything works, except the brake lights. The lights work, the turn signals work, and the emergency flashers work.

I used a circuit test light to check the harness on the car side, and that tests out perfectly. So, I plugged the trailer into the outlet on the tow vehicle, and probed the left and right positive wires about a foot past the connection with the test light, with the ground hooked to the trailer frame, and that worked. So, I am getting a current to that point.

When I tried doing the same thing on wires at the back of the trailer, and at one of the tail lights, it did not work.

Somehow, the brake lights are getting power at the front of the trailer, but not at the tail lights, but the tail lights and turn signals work, as do the emergency flashers. And, there is no break or splice between the front and back of my trailer, and it worked perfectly on my previous tow vehicle.

This just does not make any sense to me. What is happening between the first foot of my trailer wiring to the tail lights that would only make the brake lights not work, while BOTH of the turn signals and the emergency flashers work?

HELP?

CD

[parnold]

I had some flakey issues with my lights, and it turned out that I had a poor connection because I used those stupid blue crimpy things. When testing with a meter, or an LED tester, everything checked out perfect, but the lights didn't work. (also brake lights in my case if I remember correctly). The problem I had was that the lights drew enough current to make the connection fail, but the test lights, and meter did not draw enough current, so to them everything looked great. I basically redid every flipping connection on my trailer, before I removed my tailight, and discovered the source of the problem.

[tonyj]

Wait. What? New tow vehicle? Another Bentley? Pics!!!

And my guess is in the connection on the plug and play harness . Sounds like some type of voltage drop issue. Scotch-loc connectors?

[48Rob]

Some cars have a separate circuit for brake lights, independent from flashers and turn signals.

Rob

[Dale M.]

Are stop and turn signal bulbs SAME filaments (at trailer) ?.... If so, problem is in car not trailer....

If stop and turn signal firmaments on trailer are SEPARATE filaments you probably have a grounding problem with bulb holders in trailer....

Dale

[caseydog]

Some cars have a separate circuit for brake lights, independent from flashers and turn signals.

Rob

Yes, my harness has a module that deals with that. The module is working, according to the circuit tester.

CD

[caseydog]

Are stop and turn signal bulbs SAME filaments (at trailer) ?.... If so, problem is in car not trailer....

If stop and turn signal firmaments on trailer are SEPARATE filaments you probably have a grounding problem with bulb holders in trailer....

Dale

They use the same filaments. My first thought was that it had to be a problem at the car, but I've since verified that it is NOT the car.

CD

[eamarquardt]

Sumptin aint write! Sounds "impossible" but we know that "Murphy lives" and currently we know where! I think I'd make a "test trailer". Find some old tail/turn lights, wire em to a connector, and make a "pretend" trailer light system. Plug it in and see if it works. That will tell you if the problem is the tow vehicle/module or your trailer. Yes I know, it's a bit of a PITA but I think it will be easier than tearing your trailer apart or tearing your hair out. Another option is to see if a friend's trailer will work with your tow vehicle. They you'll know where the problem is.

Hope this helps.

Cheers,

Gus

[Greg M]

Have you checked the actual voltage at the output of the converter? I'm wondering if the converter has a bad transistor in it.
Is this the type that has a 12 volt input and wires that sense the lights of the car?

-Greg

[bdosborn]

Some cars are so smart now that they monitor the load on circuits. I know some new models of Dodge trucks get all wonky if you replace the stock headlights with HID type. The reduced current draw cause the ECM to shut the headlight circuit down. Maybe the increased current load due to the trailer lights is causing your car's ECM to freak?

Bruce

[glenpinpat]

my tv did the same thing. I was using a circuit tester. When I switched to a voltage meter it told me the problem was the tv. My converter was shot and needed replacing. I had even bought new lights for the trailer because I swore it was the trailer. The only other thing is to run a wire from tv to break lights and then test. The wire harness may be damaged.

[eamarquardt]

........... get all wonky ...........Bruce

For the "unenlightened: "wonky" is an industry technical term that loosely translates to "FUBAR".

Hope this helps.

Cheers,

Gus

[len19070]

Do you have amber turn signals? If so you meed an item called a "Convert-a-Light"

http://www.etrailer.com/tv-helpful_hint ... 18158.aspx

Happy Trails

Len

[Dale M.]

Any time you have lighting issues with brake/turn signals using same filament, and one works and one does not, and a converter is involved, its the converter....

Converts are the most unreliable thing man ever created and more confounding than a woman....

Dale

[Greg M]

...and more confounding than a woman....

Is that possible?

-Greg