Question on trailer lights

[rejesterd]

Hi All - My trailer is about 10 years old, and I've been having intermittent issues with the lights. When I started inspecting things last week, it was clear that the ground connection to the frame wasn't solid and the wires going to each light are pretty corroded.  So I decided to rewire the whole thing and get some new submersible LED fixtures.

 

Right now, I'm testing the 4-wire coupler on the vehicle side, just to make sure everything's ok there.  However I'm getting some unexpected results on my test light, and I want to confirm if what I'm seeing is right or wrong.

 

When I turn on my headlights with the vehicle in park, I'm getting 12V not only to the brown wire, but also to the yellow and green wires.  I've tested with my test light and a multimeter, and I get the same results.  My understanding is that only the brown should be getting 12V when the headlights are on and the brakes are not applied.  Is that correct?  Note that when I put the blinkers on, I see that my test light blinks as expected for each side (yellow and green).

 

Nothing has changed with the wiring on the vehicle side since I had my hitch installed, and the lights did generally work correctly most of the time.  But I thought green and yellow are only for the brakes and turn signals, so I didn't expect all 3 wires to get 12V.  Is what I'm seeing expected, or do I have a problem with the wiring on the vehicle side?

 

Thanks so much.

[Swagonmaster]

Try running a separate ground for a test. If there isn't a decent ground the juice tries to go to ground any way it can, as in wires that should be dead right then!

[Swagonmaster]

A question that I should have asked before, are you checking with the trailer hooked up or at the trailer hitch plug? If it's at the plug the lights on the vehicle will be acting up, if testing at the lights on the trailer again if your test is valid the vehicle lights will all be on at the same time. If there really is a issue with the trailer pluged in you have likely shorted some wires together or the lights are not properly grounded and the light that should be on at the time has electricty that is trying to ground through the filaments of the other bulbs. If it's dark enough you can  see the other bulbs in the vehicle light up very dimly. Years ago I had a 55 ford that sometimes  the dash lights would go dim and the turn signal bulbs would shine dimly because of a poor ground and the electricty had to go somewhere.

[WRB]

4 wire trailer wire: white ground, brown tail & running lights, green right turn, yellow left turn. The ground white wire connects to your trailer frame. Brakes use both of the bright turn signal lights. 

Tom

 

[rejesterd]

13 hours ago, Swagonmaster said:

A question that I should have asked before, are you checking with the trailer hooked up or at the trailer hitch plug? If it's at the plug the lights on the vehicle will be acting up, if testing at the lights on the trailer again if your test is valid the vehicle lights will all be on at the same time. If there really is a issue with the trailer pluged in you have likely shorted some wires together or the lights are not properly grounded and the light that should be on at the time has electricty that is trying to ground through the filaments of the other bulbs. If it's dark enough you can  see the other bulbs in the vehicle light up very dimly. Years ago I had a 55 ford that sometimes  the dash lights would go dim and the turn signal bulbs would shine dimly because of a poor ground and the electricty had to go somewhere.

I'm checking at the hitch plug.  I'm going to do the rewiring today with new LED lights, and see what I get.  

[haggard]

First thing to check is that you have a good ground. Measure resistance between any two points that should be grounded and make sure there's close to zero resistance on the ohm meter. If you don't have a good ground, really strange things can happen. Then check resistance between each of the 4 wires against all the others and make sure there are no shorts. That's a good starting point and if something doesn't pass it should help guide you to the problem.

 

[rejesterd]

Just wanted to update this, as I figured out the problem: it was a bad rear brake light bulb.  As soon as I replaced it, my test light started showing 12V only on the brown wire with the headlights on and the vehicle in park.  

[redmexican5081]

When you do start a rewire on the trailer, consider spending a little extra and getting a quality harness for it.  The harbor freight ones look great because of the price but the actual wire inside them will corrode away in about 2 years under regular usage. Nothing is worse than taking the time to rewire a trailer only to have to redo it in a few years because you tried to save some money on a cheap set of wires.

[Swagonmaster]

That's for sure, I went that way and had to take it all out after a few months and replace the harness with one from Northern tool.

[Maggiesmaster]

Etrailer.com sells quality trailer wiring parts.