So, you are all set to take the van somewhere and your worst nightmare comes true……. you can’t get the 13 pin plug to plug in to the socket on the tow vehicle!
I guess a lot of you have been there and this is one of the reasons there are a lot of comments like “the old 7 pin plugs are better, you never get this trouble” Well, I have to disagree. The modern 13 pin connectors are manufactured to a far better tolerance than the old 7 pin plugs, the contact pressure on the conducting surfaces is higher – how many times have you heard “well if its stiff or some of the lights don’t come on put a screwdriver in the slot in the pin and open it up a little”
The biggest problem with the 13 Pin plugs is that people don’t understand how they work and what bits twist and what bits don’t. I have put together here a few photos showing how a new plug fits and what bits twist.
The photo above shows the three bit’s that come in the packaging when you buy a new plug. Now if you have bought your caravan and it already had a 13 pin plug fitted, there is a fair chance you have never seen the green bit on the left. Well without this, you cannot “reset” your plug or take it apart. The second reason the green cap is included is it’s a fully sealed cover for the pins. If you look inside, you can see a rubber ‘o’ ring to make a dust and waterproof seal. Note, in the photo, the cable grip is in its “open” position which allows better access to the terminals for making the individual cable connections. The cable entry gland or shroud is the lighter colour section to the right hand side of the plug body, it’s made of a flexible rubber so that it provides a tight seal on the cable.
If you are assembling a plug for the first time, it can be quite difficult to get the 11 core cable through the gland as it’s designed to be a tight fit. Cable soap on the cable will help.
The photo above shows the position of the cable grip when the plug is ready to be assembled. I have not used a cable at this point as to show how the plug works, I wanted something that could not flex or rotate, so I used a pencil.
If you notice, I have taken care to line up the writing on the pencil with the moulded arrow on the core section. The reason for doing this will become apparent shortly.
To insert the core section carrying the pins into the housing, the two arrows that are moulded into the plastic (shown above) have to line up…. and this will allow the core to slide past little “pips” moulded into the plug housing. These pips are important, they allow the housing to rotate around the core section. Understanding that the housing rotates not the core carrying the pins is important.
Now we can see (above) the plug ready for final assembly. The inner core has been inserted into the housing, but not pushed all the way home yet. You can see how the two arrows and the writing on the pencil line up. This is important.
In the picture above, you can see the writing on the pencil is still in the same position as before, and still aligned with the arrow on the inner core of the plug. What has changed now is the outer housing has rotated around the inner core and cable (or pencil in this case) to the correct position. This is the final assembled position and is ready to be plugged into a socket.
In the picture above, the plug is partly inserted into a socket (this is the same fitting as installed on your car) but I have not rotated the housing yet. If you look closely, you can see I have put a white mark on the housing of the plug and on the rubber cable entry shroud that line up with the writing on the pencil. Now when we turn the housing 90 degrees clockwise to fully connect the plug, look what happens……
The housing rotates around the core and it rotates around the cable gland. The white mark on the gland is still aligned with the writing on the pencil. It is designed to do this. So now when you are plugging in your 13 pin plug into the socket on the tow vehicle, think of it like this. The pins, the cable and the cable gland are all one solid piece and the only way to connect them is to line up the pins, then rotate the housing round them.
What if the plug won’t line up correctly with the socket?
This is where you need your green cap or alignment tool. It takes a bit of getting used to, but line up the green cap with the centre section of the plug. You only have to put the cap on a few millimetres, now holding the cap steady, twist the plug housing… you might have to check which way it needs to turn by turning it gently in each direction. You should feel a bit of resistance then it should ‘pop’ over the pips.
Why does this keep happening to me?
One of the biggest causes of the plug becoming mis-aligned is “plugging” it into the moulded receptacle in the ‘A’ frame fairing. Effectively, you are twisting the plug around to insert it and as the cable is quite thick and the moulding does not have an insert to stop the inner twisting the wrong way, you inadvertently mis-align the plug housing and inner core with this twisting action.
It’s not that the plug has a design flaw, it’s that the moulded section on the ‘A’ frame fairing to store the plug is not correct. A far better way of keeping the plug safe is to use the green cap for what it was designed for… keeping the core and housing aligned ready for use and protecting the pins from the environment.
All wet lubricants are sticky to some extent and will hold grit and dust. The core of the plug that contains the electrical pins should be free to rotate and if it’s binding, it should be investigated why. One of the most likely causes is that the cable clamp has not been tightened down equally and one side is higher than the other, this will bind on the inside of the plug housing.
The core section should not normally need any lubrication, but if you feel it does, use something like Tri-Flo (you may have to search for it). It comes in two forms – as an aerosol and as a light oil. The aerosol version is the only lubricant I’d recommend for 13 pin plugs. I have used T9 Boeshield which is an aviation product (made by Boeing) with similar properties but is very expensive.
The rubber cable gland has a flange moulded into it that fits inside the housing of the plug body. Again, a tiny amount of lubricant here will allow the body and gland to rotate freely.
Remember most lubricants are conductors to some extent, so don’t flood the plug with lubricant.
Some people think that it is necessary to cover the screw terminals in grease or Vaseline or some other paste to protect them. In a quality plug, the contacts will be nickel-plated and the overall protection of these plugs from water ingress is a lot better than the old style, therefore I wouldn’t recommend it. Besides… it is always worth every season, just opening the plug up and performing a visual inspection.
Rubber ‘O’ Ring
If you find you need to replace the rubber ‘O’ ring on the plug, you can buy them via the well known auction site or from people like Screwfix Direct (selection box of O rings). The size is 40 mm diameter and 1.5 mm diameter cross section. If you have difficulty in getting them, try these guys… Polymax look for 40X1.5N70 – you will have to buy 15 of them though!
Assembly Instructions for the Menber 13 Pin Plug
A number of searches directed by Google to Caravan Chronicles are for people looking for the assembly instructions for 13 Pin Plugs. I have scanned in a copy and posted them below. If you click on the image, they will open in your browser window or you can save them to your desktop. You can use your browsers zoom function to make the images larger if required. The images are (c) Menber
I hope you found this useful and it solves your 13 pin plug puzzle!
For information on where to get a green cap read the blog post “13 Pin Plug… the green cap arrives“
There has been some speculation on some forums that using the green cap will promote condensation in the plug and some people have received advice not to use the green cap.
My take on it is this; The wide spread use of the green cap is fairly recent. In fact the official UK MENBER importer did not import green caps as a separate item until after the post above was written and I had emailed Menber in Italy and the UK importers to see if they could import the green cap on it’s own. Up to then, it was only ever supplied with the 13 pin plug in a blister pack for retail sale. So I don’t think that there is a lot of history in using the cap and people suffering condensation issues within the plug. Caravan manufacturers didn’t even supply the green cap with new caravans.
If the plug manufacturers considered that condensation would likely lead to problems, I think the cap would have been designed with a ventilation hole in it and they would not go to the expense of installing a neoprene seal in the cap. In fact, to save money, they could just supply a simple plastic ring designed for assembly or disassembly of the plug.
The electrical pins in the plug (and socket) are all nickel plated, which is an improvement on the brass contacts of the previous designs of trailer plug. If you look at the construction of the plug and socket, the tracking length of a mated 13 pin plug and socket is far greater than the tracking length of the 12N and 12S types.
I remember 15 or 20 years ago one of the accessories you could buy for the 12N socket on your car was a rubber or neoprene ‘boot’ that fitted over the socket to help protect it from the elements… there was also a matching ‘cap’ that fitted over the end of the 12N plug. I don’t recall anyone advising us not to use these as it could promote condensation and corrosion of the electrical pins. Mind you, there wasn’t the internet back then so information was much harder to come by.
When I converted the Freelander over to a 13 Pin system, I also converted my small trailer over as I didn’t want to use an adaptor. My trailer has sat outside for 18 months in all weathers with a green cap on the plug, and this evening I went out and had a good look at the plug. No sign of condensation.
So, after all that… what’s my take on it all?…. well, lets just say I put the green cap back on my trailer plug.