Australian Trailer Plug and Socket Pinout Wiring 7 pin Flat and Round

Here’s the wiring diagrams showing the pin out for the plug and socket for the most common circle and rectangle trailer connections in use in Australia. I put this here because I had a hard time finding and figuring this out for my trailers.

If you have a round connector, commiserations. Get a flat one. Why? Well first of all, which round one? There are at least 3 different 7 pin round connectors in use in Australia right now. Queensland prefers the small 7 pin round, and apparently Victorians prefer a large 7 pin round that has a completely different pinout! There is also a heavy duty 7 pin round, which is different again! Why? Oh Why? And you can chuck in a couple of older 5 and 6 pin round connectors as well just to make it more confusing (I’m not sure if they are still in use, so I haven’t bothered with them here). Plus to top it all off, sometimes the small 7 pin round is rotated so that the yellow pin is at the top!

On the other hand, flat connectors have only one possible pinout in Australia, one possible orientation (they aren’t half rotated), and the extended 12 pin version is even compatible with the 7 pin one. So every rectangular connector in Australia is compatible!

Mandatory disclaimer – I’m a programmer, not an auto electrician, so please check first 🙂 Most images are from Varta – a manufacturer of plugs, sockets and adapters sold in Australia.

7 Pin Flat

flat

(Image from Varta). The best! All diagrams are as viewed from the Cable Side. What that means is that this:

7 Pin Plug (image from Wikipedia):

Actually looks like this:

(My photo). Black and blue wires are not connected in the above image as they were not needed for this box trailer with no brakes or aux/reverse. The Earth pin (3) is slightly further away from the camera – it is a bit lower than the rest of the pins.

12 Pin Flat

This is an extension of the 7 pin flat. The 7 pin flat plug will fit into a 12 pin flat socket and work perfectly.

flat12

(Image from Varta). All diagrams are as viewed from the Cable Side – see example above

Small 7 Pin Round (QLD)

Identifying: Plug size is similar to an Australian 10c coin. There is a noticeably larger gap between 1 and 6 on this plug, though some trailer places rotate this connector that the yellow is at the top. Socket and plug are keyed.

small-round

(Image from Varta). All diagrams are as viewed from the Cable Side.

Large 7 Pin Round (VIC)

Identifying: Plug size is similar to an Australian 20c coin. Pins evenly spaced. Socket and plug are keyed.

large-round

(Image from Varta). All diagrams are as viewed from the Cable Side.

Heavy Duty 7 Pin Round

Identifying: Plug size is similar to an Australian 50c coin. Earth is bigger pin. No key (other than oversized earth pin) on the socket or plug.

heavy-duty

(Image from Varta). All diagrams are as viewed from the Cable Side.

It’s cool to be square (well, rectangular)

In my personal experience the flat style plug is more reliable. I used a small 7 pin round for 10 years, and then after replacing the plug multiple times changed to 7 pin flat for the last 15 years, and I have never had a problem with a flat connector. I had one vehicle with a 12 pin socket and a trailer with a 7 pin connector and they played happily for years.

Why is it more reliable? I think part of it is that the flat connector has the female part (the part you need to protect most) covered and attached to the vehicle, whereas the 7 pin round – although the connector has the female socket on the car, the plug on the trailer has female sockets for the individual pins. I don’t have the luxury of keeping my trailers in a garage – they are out in the elements – which is great if you like providing homes for bugs. I can’t count the number of times I had to remove critters from the trailer side of the 7 pin round connector. Not so with the 7 pin flat.

na na na na na na na na na na na na na na na na Flatman! (and Ribbon)

It might just be me, but I also think it makes more sense to have the socket powered rather than the plug (just like household 240v sockets – imagine if they were 240v prongs sticking out of your walls at home that were live).  It’s hard to short out a powered socket as you need two conducting prongs, whereas shorting out a powered plug is simply a matter of touching two of the prongs with something conductive (like a screwdriver, finger, etc).

So if you have the choice, go flat! For years in Queensland the small 7 pin round was the most common, but since about 2010, the flat has become the norm. I bought a car a few years ago and immediately had the round socket changed to a flat one, and the towbar place who fitted it said that flat had become more common.

Enjoy! And feel free to disagree / correct me in the comments 🙂

53 thoughts on “Australian Trailer Plug and Socket Pinout Wiring 7 pin Flat and Round”

  1. Incredible as it is in this day and age, each new “standard” adds to the long growing list.

    As an electrician by trade, auto wiring is tangled mess, including the weird diagrams that are intended to help. Beyond that, the simple terms plug and socket, and the male/female reference is confusing. You can have a female plug with males pins, and vice versa. If these principles were applied to lethal voltages, the death toll would be massive.

    Reply
  2. Daniel, you said you have the female round on your trailer. I have always known the female socket to be on the towing vehicle. The exception being for remote field work I have seen female sockets fitted to both the tug and the trailer and the connection is made with a cable with male plugs on both ends. This keeps the connections clean on both ends. Excellent page and well presented.

    Reply
    • You’re right. The plug on the trailer side of the round connectors is the male plug. I was unclear in the article that I was referring to the individual pin sockets on the plug which tend to get filled with bugs and gunk. Thanks heaps for pointing this out. I’ve updated the article to hopefully make it clearer. Much appreciated.

      Reply
  3. Anybody know why the crazy numbering of the flat connector.
    Why doesn’t it just number 1 to 7.
    Am I missing something?

    Reply
  4. Hi,

    So auto sparky fitted a new 7 pin flat connector in the rear of my ranger.

    Went camping and came back and the trailer wiring is totally meted.

    I opened up the new connector and it’s wired backwards. Ie pins 4 and 1 are reversed and 6 and 7 and 2 and 5. Would this cause the wiring to melt in the trailer? Just got back to taking trailer and car to sparky tomorrow

    Reply
    • It’s very confusing how all the plug diagrams are from the cable side, not as you look at them end on. I’m guessing someone wired the trailer (or car) the opposite way around. Melting sounds more like a short to me though. I’m sure the sparky can sort it out for you.

      Reply
  5. Good stuff FT. My recent experience. I have a flat 7 on the Ford. Right flash stopped working, wiring all OK, connecting screws OK. After a bit I found that, as the plug is held quite securely in the socket, I was tempted to wiggle the plug from side to side to release it. In doing so the split brass male section of the plug closed and, being brass, did not spring back thus losing contact with the female section in the socket. Simple fix; gently press a knife blade into the split to expand it and resist the wiggle.

    Reply
  6. Great post. Fully agree with flat ones. Had some time on my hands and rang the maker of the round ones. They could not tell me why the pin wiring configuration was different with other PIN numbers

    Reply
  7. I piggy backed a 7 flat and a 7 round (Vic style) together on two of my vehicles, stopped needing the adaptors, which I could never find if I needed them. I always preferred the flat, but being in Victoria most friends have the round.

    Reply
  8. trying to work out why simple logic is not used when designing and manufacturing these products….making it simple for the average person so that you do not twist their brains inside out?/.
    Thankyou.

    Reply
  9. Could you please give me the old ( 1980’s ) wiring harness colours as the currant one has differs colours the one that I have now is the standard yellow,black,white,green,blue,red, and brown. There are different colours than I have. Some have striping and some colours are just not there. I would like your help in this matter!

    Reply
    • Yep, that seems the most likely cause.

      Brakes need a lot of power. Run a separate cable – 4mm seems to be the recommended size, 6mm if running a long way.

      Hope this helps

      Reply
  10. I have 7 pin round. When I plug new van into vehicle, vehicle reverse lights and Auto indicator (R) lights come on. Even when vehicle is in park.

    Reply
  11. Hi,

    Question toon went to change from round to flat in Victoria today as the new car has flat connector on the back of it. Bought two narva 7 pin connectors to wire up to the trailer and a bike carrier.

    Found the bike carrier had its wires soldered to clips so decided not to play with it for now and just tested it with an adaptor I had from round to flat.

    All lights worked fine, brake, rear lights and indicators and discovered when you unplug the connector from the car with the car locked alarm goes off.

    It’s an Amarok if that makes any difference for below.

    When I tried to reword the flat connector to the jet ski trailer I can get everything to work but the brake lights. I only have 5 wires as no reversing and I assume no service brakes as I a, making the assumption that is electric brakes which I don’t have.

    I tried the wire in both and I can’t get the brake lights to come on. I haven’t had time to try the bike carrier again since I did this to test I haven’t blown a fuse.

    Any ideas as I have read on the net there seems to be some issues with Amarok and trailer wiring so not sure if it’s me or the car.

    Should be straightforward to match the colours I’d of thought,

    Reply
    • Perhaps the alarm going off is intended? To alert you if someone is trying to steal your trailer?

      In any case, with an alarm to complicate matters, I think I’d be going to an auto electrician to sort all that out.

      Reply
      • The alarm go’s off it sensors a change in current / voltage, it’s like sometimes you can sit in your car and arm the alarm, then turn on your interior light and the alarm will go off. As for brake light either pin #5 (blue wire) or
        pin # 6 (Red wire)

        Reply
    • many modern cars need an electronic trailer module to make things work without upsetting the body control module. Mazda’s will even shut the vehicle down if a trailer is connected without the electronic adapter

      Reply
      • Brendan,
        Is this likely to be my problem?
        I had a tow-bar fitted by the dealer about 2 weeks after I took delivery of the new car. This week I purchased a bike rack lighting bar for the new car, for my bike rack that attaches to the 50mm hitch-type tow-bar and when I connected the 7-pin flat plug of the lighting bar to the 7-pin socket on the car only the brake lights on the new lighting bar work. The rest – both indicators and the rear lights & number-plate light on the lighting bar don’t work!
        I’m taking the car back to the dealer, along with the lighting bar, next Thursday for them to sort out but would appreciate your opinion as to whether I need one of these “trailer modules” you refer to and if so whether that should have been fitted from the start by the dealer or whether the dealer will try and make me pay extra for this “trailer module “?

        Reply
  12. I have five colours on the main trailer cable yellow white green brown and red.
    But my lights have 6 colours
    Black green blue yellow red and white
    What do I do how do I connect them

    Reply
  13. Hi I have a 7 pin flat on my van rated to tow 2T & 2 the black wire is reverse lights
    Where do I get power for my on trailer Brake controler as normally it is the black wire

    Reply
  14. Why is there a wire (black) for reversing lights … when, up until recently, at least, … Caravans didn’t have reversing lights? 🤔

    Reply
  15. Totally agree – go flat! Here in WA the most common plug is the medium sized round 7 pin and the flat type is known as the Eastern States Plug. However, I use an adapter for flat to round when my trailer gets loaned out to a car with round socket. 30 years ago the WA type was 6 pin round and I have even seen setups using 3 pin mains plugs on the trailer and sockets on the car making 6 connections!

    Reply
  16. My trailer wires have 2 yellow wires one with a green stripe and one just yellow. It is a a 7 pin small that I have. I also tried but can not get reverse lights to work? the rest are working

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  17. Daniel, thanks for the information.
    This is very helpful after spending an hour and a half on trying to sort it out.
    Should have look for something like this before hand.

    Reply
  18. I totally disagree. 7 pin flat plugs are the most useless piece of plastic out – always breaking. Small seven pin round METAL plugs for me.

    Reply
  19. just taking a flat plug off the vehicle to replace it with the round.
    now wondering why I have an extra 2 wires in the lume that go to the outer sides of the flat plug.
    there is no outlet for them to plug into.
    what are they for?

    Reply
    • Hi Mick! First of all I’d stay with the flat connector, but that’s just me. If they aren’t connected, I’m guessing the extra wires are for Auxiliaries or Fog lamp or similar which is part of the 12 pin flat – even though you had a 7 pin flat the wiring loom may have included these in case you ever wanted to go to a 12 pin flat. That’s my guess, but I’m no auto electrician. If they weren’t connected I’d just make sure they are well insulated with electrical tape so they don’t short on anything. If they were connected to any metal housing they might be an extra earth return – you can check this by checking the resistance between the earth return (white) and the spare leads. Low resistance = another earth return. High (or infinite) resistance = not earth return. If not an earth return, tape up well and ignore them. Or check with someone who knows what they are talking about instead of me 🙂 I found a local towbar fitting place that fits new trailer plugs to cars for $20.

      Reply
  20. Grrrrrrr, found this picture after ripping of the whole round plug. Found the indicators are swapped and shorts out the brake lights.
    After blowing 3 fuses decided to limp back home to sort it later. Guess what, the image of the round plugs has been rotated about 150 degrees: yellow should point up.

    Reply
    • Well, I just learned something new. Apparently there is another 7 pin round – a large one that is common in Victoria, with a completely different pinout. Why did they do that? I’m in Brisbane. Also sometimes the small 7 pin round is rotated so that yellow is on top. Not sure which is your case – if the indicators are swapped it sounds like the large plug. I’ve altered the article and added the large round connector so others don’t have this problem. Thanks for letting me know, and sorry.

      Reply

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