Trailer Wiring question

Discussion in 'General Automotive Tech' started by zzzizxz, Dec 2, 2018.

  1. zzzizxz

    zzzizxz Well-Known Member

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    Hey all,

    On my 1981 Pontiac Safari, it looks like it was set up to tow. I have the auto leveling air shocks in the rear, as well as what looks like a 4-pin trailer wiring connector under the rear bumper.

    My issue is that while it looks like a 4-pin connector, it is much larger than a standard 4-pin. I've tried looking to see if there is a connector that goes from my oversize to the standard, but have come up with nothing.

    Here's a picture with a standard trailer connector, the larger one that is on the car, and my finder for scale.

    Before I start cutting wires back there, can anyone shed any light on whether they used to use larger connectors in 1981?

    Thanks!
     

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  2. Silvertwinkiehobo

    Silvertwinkiehobo "Nothing is foolproof as fools are ingenious."

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    A) That has to be aftermarket, as I'm reasonably sure a factory GM connector would've been a Weatherpak connector, and B ) I think, if finding an adapter is difficult, you likely should just swap in a smaller 4-pin connector, just to stop the headaches of dealing with this one.
     
  3. HotRodRacer

    HotRodRacer Well-Known Member

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    Ya'll really can't count, can you? :LOL:

    Well, here's the scoop - the one on the bottom is the standard 4 pin connector (brakes, left/right signal and tail lights). I don't know if this is your trailer connection or the wagon connection.

    The one on the top is a five pin connector. The fifth pin ties into the backup lights for energizing a solenoid for a trailer with tongue brakes. If you didn't have it, when you tried to back up, the brakes would lock because of the weight pushing forward on the tongue. That fifth pin energizes and closes the solenoid to keep the brake fluid from flowing through the lines to the brakes. It beats the heck out of trying to put the manual lock pin in place to back up a heavy trailer.
     
  4. Silvertwinkiehobo

    Silvertwinkiehobo "Nothing is foolproof as fools are ingenious."

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    In my defense, I was concentrating on the four-pin.
     
  5. zzzizxz

    zzzizxz Well-Known Member

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    Ha! I don't know how I missed that extra pin there. I blame that on having a 6-week old baby...

    I guess my new question is, shouldn't I be able to plug a 4-pin connector into the 5-pin? If the last pin is for trailer brakes, I just wouldn't use that last pin. But the 4-pin from the trailer is too small to plug into the 5-pin on the car.

    Is there some other connector I need to use to upsize the trailer connector?

    Thank you!
     
  6. HotRodRacer

    HotRodRacer Well-Known Member

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    Well now, you got me there. I didn't even notice the plug was smaller on the trailer! I'll have to blame that on not paying attention! ;)

    I have never seen the style of trailer connector that is in your pic. The short answer is yes, you should be able to plug a standard 4 pin trailer connector into a five pin vehicle connector with no adapter required. As you said, the reverse light/electric brake solenoid just isn't used. Now I am wondering what the heck the trailer connector actually is - could it be a European Cobra trailer connector?

    Look at this on slide 13 for example.

    Beats the heck out of me, buddy. That's strange indeed. The next step I'd probably take would be to put a standard flat-4 connector on the trailer end side.
     
  7. joe_padavano

    joe_padavano Well-Known Member

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    IMG_20181206_102133914.jpg You all should read the factory service manual. The optional factory trailer harness on these cars is a four wire pigtail. It didn't come from the factory with any connector. This pigtail plugged into the four pin connector at the license plate. That four pin connector is not intended to be the connector to the trailer. Someone lost the mating pigtail - it may still be on the trailer that was towed previously.

    Edit: Nice forum software that flips the photo when you attach it... :rolleyes:
     
  8. zzzizxz

    zzzizxz Well-Known Member

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    Thanks Joe!

    So I guess my best bet is to cut off that extra large 5-pin that is on the car now, and install a standard sized connector?
     
  9. HotRodRacer

    HotRodRacer Well-Known Member

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    Joe - the flat-5 connector is on his car currently, not the small four pin. The small four pin is the lead from the trailer.

    zzzizxz - if it were mine, I would leave the five pin connector on, and cut off the smaller 4 pin one that is on the trailer and put a standard flat-4 on it. The four pin will plug into the five pin and work with no problem. Joe may have different ideas.
     
  10. zzzizxz

    zzzizxz Well-Known Member

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    The problem is that I cannot find a 4-pin that will fit the 5-pin.

    The 5-pin that is on the car is 2 inches across. The 4-pin on the trailer, and the 4-pin flat adapter I bought are both only 1 inch across, and they both seem to be standard sizes, not the small size.

    Since the 4-pins are half the size of the 5 pin, I cannot plug them into the 5-pin on the car.

    What am I missing here?

    I feel like I'm missing something glaringly obvious!
     
  11. HotRodRacer

    HotRodRacer Well-Known Member

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    That's strange - here is the utility trailer currently hooked up to my Silverado:
    upload_2018-12-6_15-55-39.jpeg

    Here is the flat-4 connector from the trailer plugged into the flat-5 on my truck:
    upload_2018-12-6_15-56-23.jpeg

    Unplugged to show size and detail:
    upload_2018-12-6_15-56-56.jpeg
     
  12. HotRodRacer

    HotRodRacer Well-Known Member

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    I had to trim the end of the trailer plug off because it had the plastic shield all the way around it, but after that it fits perfectly.
     
  13. zzzizxz

    zzzizxz Well-Known Member

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    Would you mind going back out and measuring how far across your 5-pin is, from outside of the first pin to the outside of the last,
    And also measure your 4-pin?

    This may just be as simple as my being an idiot and getting the wrong connectors. I did miscount how many pins were on the car after all!

    Thank you!
     
  14. HotRodRacer

    HotRodRacer Well-Known Member

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    Don't mind at all - hold please...
     
  15. HotRodRacer

    HotRodRacer Well-Known Member

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    Flat-4 on trailer end:
    upload_2018-12-6_16-11-49.jpeg

    Flat-5 on truck:
    upload_2018-12-6_16-12-12.jpeg
     

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