Forum Discussion

Djsrcy's avatar
Djsrcy
Explorer
May 09, 2018

7pin wiring problem. Please help!

I have a new to me travel trailer. I am having a few issues with the wiring. Let me list those and then I'll list what I have done so far.
1. When headlights are on, running lights are not.
2. When I hit the brakes, the running lights come on.
3. When I use right turn signal, running lights flash.
4. left tail light is out completely.

Here is what I have done.
1. I have confirmed the tv wiring is fine.
2. I cut the 3 grounds that were attached to the trailer near the front. I restripped, added new ring connectors, cleaned up the contact point on the trailer, and used a new screw.
3. Did the same for the grounds coming off of each tail light going to the frame.
4. I replaced both rear bulbs.
5. I pulled off the tail light housings and cut and redid the connections for those too.
6. I replaced the 7pin plug.
7. Opened the junction panel under the camper and everything LOOKS good.


I was and kind of still am convinced that this is a ground issue but have no idea what to check or how to check it. Been messing with this for days. At my witts end. ANY help is appreciated.

Thanks, Djsrcy
  • Djsrcy's avatar
    Djsrcy
    Explorer
    May 10, 2018
    YC 1 wrote:
    Grab a battery jumper cable and find a shiny place on the tow vehicle and then make a shiny place on the TT frame. Connect.

    Once you have an absolute known good ground you need to start over.

    IF you can open the TT plug while it is plugged into the tow vehicle you can then use a test light to check each pin. Use a 12 volt test light and make sure it shows as brightly on each connection. A voltmeter will lie to you.

    Once you are sure the tow vehicle is sending proper signals then go back to any of the tail lights and begin testing there.

    Once you have this sorted out you can pull the jumper cable off and if things change you can then address that.


    I will buy a test light tomorrow and open the housing on the 7 pin.
    I'm not sure what you mean by "go back to the tail lights and begin testing there" test what/how?
    thanks
  • Djsrcy's avatar
    Djsrcy
    Explorer
    May 10, 2018
    Artum Snowbird wrote:
    If you take the red covers off the lights you will find that the brake/turn filament in the faulty grounded bulb glows faintly when you brake, and the running lights glow brighter. What actually happens is the positive current comes to the brake filament and wants to go back to neutral. But it can't because the ground is not good on that socket. The current then goes through that running light filament in reverse, then across to the other running light filament and through that running light and to ground.

    The running lights glow brighter than the brake/turn filament because you have three filaments all in series at that point. But you are feeding three filaments with a single 12 volt feed. The running light filaments are smaller than the brake filaments, and therefore cause a larger voltage drop across their filaments.

    Take a wire from your battery negative and touch it to the metal side of the bulb holder, put on the turn signal, and everything will work fine.

    And, I think you will find the loose connection is where the negative wire connects to the socket.


    Ok so...
    there was zero glow in left tail light with brakes pressed in. I ran a wire form wifes cars negative termnal to the tail light that isnt working.
    with headlights on the tv, still nothing at tail light.
    with left turn signal on the tv, i got the signal to work.
    the running lights still flashed with right turn signal
    running lights still didint come on with just head lights on the tv.
    running lights still came on with brake lights.

    so the only thing i got to work with a wire from negative terminal is left turn signal. Wire wouldnt reach right tail light. could both be bad? I will get a longer wire tomorrow and do same test to right tail light i guess..?
    UGH
  • YC_1's avatar
    YC_1
    Nomad
    May 10, 2018
    Grab a battery jumper cable and find a shiny place on the tow vehicle and then make a shiny place on the TT frame. Connect.

    Once you have an absolute known good ground you need to start over.

    IF you can open the TT plug while it is plugged into the tow vehicle you can then use a test light to check each pin. Use a 12 volt test light and make sure it shows as brightly on each connection. A voltmeter will lie to you.

    Once you are sure the tow vehicle is sending proper signals then go back to any of the tail lights and begin testing there.

    Once you have this sorted out you can pull the jumper cable off and if things change you can then address that.
  • Artum_Snowbird's avatar
    Artum_Snowbird
    Explorer
    May 09, 2018
    Yes, any. I think what you are saying is that perhaps the trailer is using the skin as the ground. You can try just connecting the socket to the new connection you made, see if that helps.

    As I said, if you see the faint glow of the brake filament (the thick one) and a brighter glow of the run filaments (the thin ones) the ground on that socket is the problem.
  • Djsrcy's avatar
    Djsrcy
    Explorer
    May 09, 2018
    this trailer didn't come with a battery and pop ups battery is dead. ugh! Could i use my tv battery for the test? If so, what kind of "wire" from negative to bulb holder? any?
    Thanks
  • Ava's avatar
    Ava
    Explorer
    May 09, 2018
    The post above is right on, and as said, grounding issues are usually the number one problem.
  • Artum_Snowbird's avatar
    Artum_Snowbird
    Explorer
    May 09, 2018
    If you take the red covers off the lights you will find that the brake/turn filament in the faulty grounded bulb glows faintly when you brake, and the running lights glow brighter. What actually happens is the positive current comes to the brake filament and wants to go back to neutral. But it can't because the ground is not good on that socket. The current then goes through that running light filament in reverse, then across to the other running light filament and through that running light and to ground.

    The running lights glow brighter than the brake/turn filament because you have three filaments all in series at that point. But you are feeding three filaments with a single 12 volt feed. The running light filaments are smaller than the brake filaments, and therefore cause a larger voltage drop across their filaments.

    Take a wire from your battery negative and touch it to the metal side of the bulb holder, put on the turn signal, and everything will work fine.

    And, I think you will find the loose connection is where the negative wire connects to the socket.
  • Djsrcy's avatar
    Djsrcy
    Explorer
    May 09, 2018
    I used a plug in tester on the tv. everything worked fine. I also have a popup and all of its functions work
  • Old-Biscuit's avatar
    Old-Biscuit
    Explorer III
    May 09, 2018
    First thing......
    Use a voltmeter and 'check' each blade on vehicles 7 pin plug that they are correct and functional



    Vehicle plug wiring correct.......
    Then check that trailer wiring is correct

    Use a jumper wire with male spade terminals crimped on each end
    Plug one end into the 'trailer battery' position (11 O'clock when looking at end of trailer umbilical cord)
    Plug other end into each of the other positions (except Ground---5 O'clock)

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