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Tiggs's avatar
Tiggs
Explorer
Oct 08, 2013

7-Pin Plug/Trailer Lighting Problem

I was trying to trouble shoot a problem where my running/clearance lights weren't working when the license plate light bulb was plugged in. All my other lights were working fine and dandy.

Because I accidently drug my cable down the road, I had replaced the plug and rewired the seven pin cable through a junction box where I used crimped end connectors placed over the pins of the box, like colored wires on each pin. This gave me an easy point of access to test the lights.

I wanted to isolate the trailer wiring from the TV wiring to pinpoint the cause so I tested the trailer wiring using a 12V power pack. I attached the negative clamp to the trailer frame and made a test wire that I could clamp to the positive lead and clip to the various pins. I was able to test all my lights, even my clearance running lights, which worked with the back up bulb plugged in.

Then I checked continuity from the end of seven pin plug on the trailer side and all of the pins. Everything is hunky dory.

My nephew has a 7 pin plug on his vehicle so we plugged the trailer into his receptacle. Nothing worked. I unplugged the trailer plug and tested his pins with a light tester. They all work.

I went back to retest the lights with the 12V battery just as before and now nothing works. I've verified the 12V is putting out 12V, I've verified my test lead is still operational.

What have I done? Is there a fuse of some sort that I might have blown or something. If I thought it would help, I'd cry.

Carolyn

10 Replies

  • wittmeba's avatar
    wittmeba
    Explorer
    Oct 13, 2013
    Good catch, Chris. There are several on the web that are incorrect.

    # Color Gage Circuit Function connector interior
    1 white 10 common ground Tow Vehcle Connector
    2 blue 12 electric brake
    3 green 14 tail/running lights
    4 black 10 battery charge (+)
    5 red 14 left turn/stop
    6 brown 14 right turn/stop

    Not commonly used
    7 yellow 14 auxiliary/back up
  • wnjj's avatar
    wnjj
    Explorer II
    Oct 13, 2013
    Tiggs wrote:
    I hitched up the TT to the TV and connected the 7pin plug. All my lights work, even the clearance lights and the license plate lamp. I can't believe that it was looking for the additional ground from the vehicle but it appears that is so?

    Carolyn


    You need to add a wire to your splice on the ground wire to a loop terminal which you clamp under a bolt.
  • Chris_Bryant's avatar
    Chris_Bryant
    Explorer II
    Oct 13, 2013
    opnspaces wrote:
    Not doubting you, but your pin numbers and colors sound wrong compared to this diagram.

    Link



    The colors on that diagram are wrong.
  • wittmeba's avatar
    wittmeba
    Explorer
    Oct 13, 2013
    opnspaces wrote:
    If the lights only work correctly when hooked to the vehicle then you're not wired correctly.
    Hooking to the hitch is not providing an extra ground, it is providing the ground.

    If this is what happened the statement is accurate.

    You should NEVER use the hitch to serve as the ground connection. Some states (California for sure) said this is illegal back in the 1970's - I believe. You must use a dedicated ground wire thru the connector.

    You can use the trailer frame for ground for any trailer wiring. You can use the TV frame for any TV wiring. But once you encounter the plug, there needs to be a dedicated wire in the connector for ground. In the case of a 7 pin connector it is pin #1. You show connecting the TV + (black) to pin #1. Perhaps the listing is incorrect for the mapping of pin to wire color.

    Id be surprised if the lights work as the posted connections do not match any standard connector Im familiar with. Almost, if not, every wire color is incorrect. I would not connect to another TV or hook the TV to another trailer - assuming as you indicate they work.
  • opnspaces's avatar
    opnspaces
    Navigator II
    Oct 13, 2013
    If the lights only work correctly when hooked to the vehicle then you're not wired correctly.
    Hooking to the hitch is not providing an extra ground, it is providing the ground.
  • westend's avatar
    westend
    Explorer
    Oct 12, 2013
    Tiggs wrote:
    I hitched up the TT to the TV and connected the 7pin plug. All my lights work, even the clearance lights and the license plate lamp. I can't believe that it was looking for the additional ground from the vehicle but it appears that is so?

    Carolyn
    Yes, the lamp circuits need reference to ground from the same source that is powering them, i.e. the towing vehicle.
  • Tiggs's avatar
    Tiggs
    Explorer
    Oct 12, 2013
    I hitched up the TT to the TV and connected the 7pin plug. All my lights work, even the clearance lights and the license plate lamp. I can't believe that it was looking for the additional ground from the vehicle but it appears that is so?

    Carolyn
  • opnspaces's avatar
    opnspaces
    Navigator II
    Oct 11, 2013
    Not doubting you, but your pin numbers and colors sound wrong compared to this diagram.

    Link

    Ignore the colors for a minute. Does your tow vehicle socket match the tow vehicle outside diagram (left picture) in the linked post? If not I would rewire it so that it does.

    Then unhook all the wires from the plug on the trailer umbilical cord. and wire it up again to match the tow vehicle plug.

    Also I don't think the center plug is used very often and wonder if you've accidentally wired something wrong there.
  • Tiggs's avatar
    Tiggs
    Explorer
    Oct 09, 2013
    Yes, I did verify that the proper light came on. I had all the lights working prior to my chewing up the cable. I had all but the clearance lights working when rewired everything through the connector box and had it hooked up to my own tow vehicle -- except the original problem on the clearance lights. I had all the lights working, even the clearance lights w/license plate light using the 12V power supply.

    From the trailer side, the lights were working on the following wire colors. I used the same colors at the connector box to the 7 pin plug. I've also listed the pin # where the wire appears. I've verified that the pin # goes to the correct wire color at the connector box and that I have continuity through the new cable length.

    Brown is right turn signal to pin # 2
    Blue is electric brake to pin # 3
    Red is left turn signal to pin # 5
    green is running lights to pin # 6
    yellow is aux. power to pin # 7
    black is 12V to pin # 1
    white is ground to pin # 4

    If there is a circuit breaker for the 7 pin connections in the distribution center, it isn't labeled as such. I've even pulled the fuse from the 12V deep cycle house batteries to see if I blew it.

    Carolyn
  • opnspaces's avatar
    opnspaces
    Navigator II
    Oct 08, 2013
    Sounds like either a fuse or a ground problem to me. When you originally checked the trailer and truck connectors, did you verify that the correct lights came on and not that just a light comes on? I once worked on wiring a boat trailer that I sold and the buyer had obviously not consulted any kind of schematic when he wired a plug to his truck.

    Actually now that I think about it I wonder if you have some automatic resetting circuit breakers? This is based on the fact that the lights seem to work one minute and not the next.

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