Trailer wiring questions

Submitted: Monday, Mar 18, 2013 at 15:34

ThreadID: 101164 Views:6955 Replies:10 FollowUps:12

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Trailer Wiring Diagrams

This is a basic reference article about trailer and caravan wiring; the plugs and sockets that are commonly in use in Australia, and the pin colour codes that are designed to coordinate proper

Member - Rich

Hi,
Been testing the lights on my trailer as they did not work when plugged in to the car and have a few questions on how it all works

I have been looking on the web and there seems to be mixed opinions on how the trailer is actually earthed.
Some say via the tow ball
Some say via the chains
Some say via the earth wire in the plugs (what I thought would have been the one)

Can some one please tell me which of the above is correct or the standard, perhaps all are? Mind you if you have grease on the tow ball then you would lose connectivity

Another question is how can I test if the trailer plug is OK. I know how to verify the car side is working but am unsure how to test if the trailer plug is working or not .

By the way after testing etc and cleaning the tow ball and separating the trailer plug pins a bit all was good.

Thanks in advance,
Richard

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Reply By: allein m - Monday, Mar 18, 2013 at 15:58

Monday, Mar 18, 2013 at 15:58

I bought a cheap test plug from Kmart long time ago it is like a pencil and with the plug on the car I just got some one to put the brake on so I can put the test light onto each pin on the plug checking to see if each one worked and were in correct position
so you earth the test light and then with positive side you touch each pin

if you do not have a test light you can make them but kmart one is cheap as chips well worth keeping in your tool box

AnswerID: 507047

Follow Up By: allein m - Monday, Mar 18, 2013 at 16:01

Monday, Mar 18, 2013 at 16:01

Wiring Harness Conversion - U.S. to European
09/03/2009 9:53 AM

I have just moved from the US to Europe. As part of this we brought our car (a 2009 VW Tiguan) and a small boat trailer to Europe. To have the trailer registered I had to equip it with European standard tail lights with separate running lights, turn lights and stop lights. Easily done.

My problem now is how to convert the trailer hitch wiring harness and split the turn and stop lights. The local VW dealer had an easy solution: new wiring harness, cost: $2,500! It has to be an easier (cheaper) solution.

The car putlet has the US standard 7 pin configuration:

1. Turn/stop Right

2. Turn/stop Left

3. Running lights

4. Ground

5. Electric break

6. 12V

7. Spare

The trailer now has the standard European plug:

1. Turn right

2. Turn left

3. Stop lights

4. Running lights

5. Ground

6. 12V

7. Spare

A solution also has to work when both stop and one turn light is active at the same time. Any suggestions?

FollowupID: 784205

Follow Up By: Member - Rich - Monday, Mar 18, 2013 at 16:34

Monday, Mar 18, 2013 at 16:34

Hi I have one of the test lights and have verified plug on car
What I am trying to find out is how to test the plug on the trailer side

Thinking of taking cover off trailer plug then plug in and use test light direct to wires in the plug

Rich

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FollowupID: 784210

Reply By: Member - Frank P (NSW) - Monday, Mar 18, 2013 at 16:19

Monday, Mar 18, 2013 at 16:19

Richard,

The earth should be via a wire in the plug. I'm not sure if that is a legal requirement for light trailers and those without electric brakes, but it is the sensible way to go. Earthing via the hitch or chains can be intermittent, resulting in lights not working when they should.

You don't say how heavy your trailer is, but if it requires electric brakes then the NSW requirement is that earth MUST be via a wire in the plug - it is illegal for it to be via the hitch, ball or chains.

Cheers

FrankP

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AnswerID: 507049

Follow Up By: Member - Rich - Monday, Mar 18, 2013 at 16:30

Monday, Mar 18, 2013 at 16:30

Only 6x4 box trailer
There is an earth wire as also tow a van with electric brakes

Thanks
Rich

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FollowupID: 784208

Reply By: Hi-ryder - Monday, Mar 18, 2013 at 17:41

Monday, Mar 18, 2013 at 17:41

Hi Rich The correct standard is through the plug . Seven pin flat the earth in the middle one . Its normally a white wire . pending on how old the trailer is but white is standard for earth on a trailer . To know if its working stick the alligator clip of your test light into that one and the test light into the light which will be two from the left or right pending weather its mounted upside down or not . But you need lights on . If its a round seven pin earth is number 3 . On a box trailer the earth is normally in the lights . Hope that helps alittle

AnswerID: 507052

Follow Up By: Hi-ryder - Monday, Mar 18, 2013 at 17:44

Monday, Mar 18, 2013 at 17:44

Also Rich sometimes you have to split the pins alittle to get a good connection or/and spray alittle wd40 .

FollowupID: 784215

Reply By: Kris and Kev - Monday, Mar 18, 2013 at 18:09

Monday, Mar 18, 2013 at 18:09

Rich
As others have said, should be earthed via the plug. Older trailers were earthed via the body and then the tow ball, but that was prone to problems with getting a good earth. Same goes for each light where the earth is made by bolting it to the frame rather than running the earth wire to each light. Trailer lights can be a real pain. I changed my box trailer lights to LEDs and they are brilliant.
The trailer plug is also a pain. Maybe just take it apart and check all of the connections. The wires do tend to work loose. Sometimes it is just as easy to buy a new plug and start afresh. To test without connecting it to the car I just use a car battery and wire with small clips and test each pin.
Best of luck. Kevin

AnswerID: 507054

Follow Up By: Member - Rich - Monday, Mar 18, 2013 at 19:32

Monday, Mar 18, 2013 at 19:32

Kev,
Thanks for the reply.
Testing the trailer plug while not connected is what I want to do. I am across the wiring layouts. I know how to test the car plug.

Do you think the following would work as well?

Pull the trailer plug apart as you mention and:

1) do a continuity test with a multimeter OR
2) plug it in to the car and then use the circuit tester by earthing it to the car and then test each pin via the uncovered wires.

It is a new trailer.

The lights are working now after I fiddled with the plugs a bit as mentioned above but has happened before and will happen again on the trailer or van so trying to be prepared.

Rich

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FollowupID: 784226

Reply By: Shaker - Monday, Mar 18, 2013 at 18:19

Monday, Mar 18, 2013 at 18:19

Do any of the lights work?

AnswerID: 507056

Reply By: RodandJulie - Monday, Mar 18, 2013 at 18:56

Monday, Mar 18, 2013 at 18:56

Hi Richard,
If you pull yout trailer plug apart it should have,
1 Left indicator----Yellow
2 Auxlilary or reverse---- Black
3 Earth----- White
4 Right indicator----- Green
5 Electric brakes----Blue
6 Stop lights-----Red
7 Tail, Number plate and Clearance lights-----Brown

This is standard for 7 or 5 pin plugs.
Please note in a 5 pin plug 2 and 5 are not used but the colours are the same
Cheers

Rod.......

AnswerID: 507060

Follow Up By: Ross M - Monday, Mar 18, 2013 at 19:52

Monday, Mar 18, 2013 at 19:52

Well done Rod>
With that he has all he needs to know.
I can't work out why some are talking Europe and USA.

Ross M

FollowupID: 784229

Follow Up By: Shaker - Tuesday, Mar 19, 2013 at 07:55

Tuesday, Mar 19, 2013 at 07:55

7 pin & 5 pin are not the same!
7 uses 1 & 4 for indicators, 5 pin uses 2 & 5.

FollowupID: 784260

Follow Up By: RodandJulie - Tuesday, Mar 19, 2013 at 21:50

Tuesday, Mar 19, 2013 at 21:50

As I said ''Please note in a 5 pin plug 2 and 5 are not used but the colours are the same''

Cheers

Rod....

FollowupID: 784353

Follow Up By: Shaker - Tuesday, Mar 19, 2013 at 23:52

Tuesday, Mar 19, 2013 at 23:52

5 pin does use 2 & 5 for indicators.

FollowupID: 784359

Reply By: Member - Peter H1 (NSW) - Monday, Mar 18, 2013 at 19:35

Monday, Mar 18, 2013 at 19:35

If you go to "Articles" in the header near Home and go to Trailer wiring diagrams.
Article ID Number 94508

You will find all you need to know.

Peter

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AnswerID: 507067

Reply By: Member - Rich - Monday, Mar 18, 2013 at 19:37

Monday, Mar 18, 2013 at 19:37

To all above thanks for info.

I am putting it all together and hopefully resolve my problem.

As mentioned in a response above
It is a new trailer (i could take it back to the dealer but wanted to be sure it was the problem first)

I am across the wiring layouts - the trailer plug has 5 wires - missing the blue and black one.

I am trying to work out how to test the trailer plug while not connected to the car. I think I have some ideas now.

It all works now after I fiddled with the trailer plug prongs (not sure what they are called) as mentioned above (the pins do get squashed together)

Many thanks

Richard

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AnswerID: 507068

Follow Up By: Shaker - Tuesday, Mar 19, 2013 at 19:02

Tuesday, Mar 19, 2013 at 19:02

You can test the trailer by using a battery & test leads. Clip one lead to the negative terminal on the battery & the other end to the earth terminal in the plug or an earth point on the trailer, clip the other one to positive & use the other end to touch on each of the plug terminals.

FollowupID: 784335

Follow Up By: Member - Rich - Tuesday, Mar 19, 2013 at 20:08

Tuesday, Mar 19, 2013 at 20:08

Shaker,
Will give this ago.

I should be able to use the battery recharger instead of a battery (a Projecta which has a mode similar to a battery).

Richard

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FollowupID: 784341

Reply By: olcoolone - Monday, Mar 18, 2013 at 19:54

Monday, Mar 18, 2013 at 19:54

All trailers have to comply with Australian Standard AS 4177.5–2004 and in Australian Design Rule 42/04....... it states couplings and chains are not acceptable for trailer earthing, all return earthing has to be through an acceptable plug and socket.

AnswerID: 507070

Reply By: Member - Andrew - Tuesday, Mar 19, 2013 at 13:01

Tuesday, Mar 19, 2013 at 13:01

Hi Rich

To test trailers off the vehicle, I have battery powered test unit that resembles a 7 pin plug with a flat section containing a panel full of LED's to indicate what circuits are working. Cost about $30 years ago from Bursons or Repco.

It sounds like you are describing either closed up pins that aren't contacting enough or dirty/corroded pins that are being cleaned just enough by you connecting and disconnecting the plug.

To fix the first, spread the slots in the pins slightly with a small screwdriver.
The second is either a spray with one of the magic cleaners or very gentle abrasion with a fine wire brush. If you must use emery paper for this, make sure you clean all the residue afterwards. Just remember that abrasive cleaning can remove some of the protective coating and promote faster recontamination.

regards

A