12S electrics plug

[Stuckinthemud]

When I was at the van the other day, I noticed that the middle pin on the 12S plug had come loose. I bought a new plug and went over to the storage today to replace it. When I removed the plug, I could see that the black plastic surrounding the centre pin had melted at some point, allowing the pin to slide out of place. While I was wiring the new plug, the bloke on the plot next to me turned up. As caravanners do, we started talking, and when he saw what I was doing, he said: "I'll have the same job to do, soon, I guess". He showed me his plug and, lo and behold, exactly the same problem. Now, how many coincidences are there here? His van is a newer version of mine, an Elddis Crusader Siroccco. He thought his had got overhot when towing with his fridge freezer switched on. I don't think I've ever towed with mine switched on. Can anyone shed any light?

 

[Zbungle]

The centre connector on a 12s plug/socket is usually used for the earth return of the fridge. The problem with both 12n and 12s plugs and sockets is that they are plugged together with a fair amount of 'wiggling'. This causes the pins on the plug to get compressed (it's not solid brass, they have a slit down the middle). In its compressed state the pin does not make a very good contact with its corresponding tube and so electrical resistance develops. This resistance is converted to heat and you get the sort of melt-down that you and your neighbour have experienced. I would go as far as to say that most of us have experienced this sort of melting at some time in the past. You say you have never towed with the fridge turned on, well, I can't explain that. To ensure that you don't experience this melting of the plug in future, (whether you use the fridge or not) occasionally check the plug and use a small bladed screwdriver to gently push into the slit on the central pin and make sure that you maintain a gap.

 

[AlanJ]

Hi
This is quite common on the 12S socket - it is called "Pin 7 BurnOut". It happend to me this year whilst away in France.
Lucky I always carry both 12N & 12S plug and sockets in my spares pack.
I also took the opportunity to carry out the following modification on the 12S caravan Plug which will prevent this occuring in the future.
Wiring outlined here http://www.motabars.co.uk/burn_out.html
Regards
Alan J

 

[Guest]

As has been mentioned this is a common problem, and has just happened to me while here in Spain. I have had to get a replacemnt sent to me by my son as 12S plugs are thin on the ground in Spain.
However as I have plenty of time here I have investigated my set up and discovered some anomalies. The van is a EU van and originally had 13 pin wiring but because it was imported and sold in the UK the dealer (bless his socks) changed it to the 12N and 12S system. Of course my tow car has a 13 pin socket so I have had ot use adapter cables, but they have not been a problem. At first teh fridge did not work on 12 volt and we discovered that Volvo had forgotten the relay when they did the towbar (bless their socks too) They installed the relay with mucho apologies and the fridge worked fine, for about a season then stopped again. Checking and I discovered the centre pin in the 12S plug had melted and a connection exsted to a side pin where there wasa 12 volt supply. Ergo, fuse blown in car.

Bactracking in the van and I discovewred that the earth for the frdige was the black wire attached to pin 7, the melted one. However the dealer (bless his socks again) had used 7 core grey cable where the black wire is only 1 mm and so was not strong enough for the fridge. The thick white earth wire he had used to earth the direct 12 volt feed, which is accepted as a correct way to do things, but the fridge was wrong. Reading my caravan manual revealed that the original 13 pin set up used the white earth as a common earth to both 12 direct feed and 12 volt ingniton controlled frdge feed so what I have done is used this white wire as the earth for the fridge but have kept the black wire disconnected until I replace the grey cable with 5 core which had 2.5 mm wires for all the colours. I have a battery fitted to the van so the lights always work etc and the necessity to charge the battey from the car is not that important as it will be charged on site. I could also connect the white earth to both earth terminals as described in my book but will probably use the new 5 core cable instead. The white earth cable is to pin 3 so is not subject to the same abuse as the centre pin and I feel this is better

 

[Stuckinthemud]

Well, this is why I LOVE this site. Not only do you find that you're not alone with a problem, but someone comes up with a solution. Thanks to all the contributors. I have used the spare brown wire on the 12S socket for an additional earth, and have bridged pin 7 in the 12S plug with the relevant pin to double the earth from the fridge. Brilliant!