12S Plug and Socket Overheating

Have you experienced any problems with the centre pin of the 12S plug and possibly also the socket overheating. From the 1999 model year the wiring of the 12S plug and socket was changed. One effect of this was that the centre pin (pin 7), which was formerly unused, became the return pin for the fridge. This has to cope with a current of around 10 amps. This is fine if everything is shipshape but likely to lead to overheating if the connection is less than perfect. There are two possible scenarios that can cause problems.


If your towcar was originally wired to the pre 1999 standard and then subsequently modified it is possible that the modification was incorrectly done. It is even possible that some new cars could be incorrectly wired. Basically there should a dedicated earth wire from pin 7 on the socket to a good earth point on the tow vehicle. However it is not unknown for pin 7 simply to be connected to pin 3, which is already earthed. This arrangement can put an overload on the wire to pin 3 as newer fridges tend to take more current from the car than pre 1999 models. This can cause the wire, and possibly pins 3 and 7, to overheat.

1: Working plug.


2: Damaged plug side a


2: Damaged plug side b

Assuming pin 7 on the socket is correctly wired back to a good earth on the tow vehicle, it can still overheat. Being the centre pin, pin 7 is set forward from the other pins such that acts as a guide when the plug is inserted.


This overheating can be serious enough to damage both the plug and socket but usually it is the plug that takes the brunt of the damage. The area around the pin becomes softened and darkened and the pin may be pushed back or even pulled out from its normal position. Once the plug is damaged in this way it should be replaced but how can a recurrence of the problem be avoided?


Fortunately there is normally at least one unused pin that can be brought into play to share the fridge return current with pin 7. Pins 2 and 5 are usually unallocated but pin 5 is sometimes used by caravan manufacturers as part of any alarm system. My recommendation would therefore be to use pin 2, assuming that it is free. All you need to do is to connect pin 2 to pin 7 both at the plug and at the socket.


This arrangement shares the current and greatly reduces the chances of overheating problems. It also has the advantage that the towcar and caravan are still compatible with other 1999 or later caravans and towcars, albeit without the extra protection.


If you don’t fancy messing around with the wiring then you can just carefully prize apart the squashed leaves of pin 7 using a stanley knife or a small instrument screwdriver. Be very careful when you do this not to open the leaves up too far as they are normally very brittle and will easily snap off, requiring a new plug to be fitted. If successful this should restore normal contact for a while but the leaves will eventually get squashed together again so this procedure cannot be regarded as a permanent solution.


If you think you may have either of the problems outlined above then call Total Caravan Care and we’ll sort the problem.

Liquefied Petroleum Gas (LPG)

What is the difference between Butane and Propane?

Butane and Propane have slightly different properties, the most important to the caravanner being the boiling point at atmospheric pressure. In other words, the temperature at which it changes from being a liquid to being a gas. Butane will only readily change to a gas above 0°C, so is generally suitable for the spring to autumn caravanner. Propane, on the other hand, will become a gas down to – 40°C and therefore can be used in winter, or all year round if desired. In UK Propane is generally sold in red cylinders, Butane in blue.

Thinking of buying a used caravan?

Has it been serviced and is it fit for towing? Is it damp?


We have seen many instances where unsuspecting people have bought what they thought was a little gem only to find out that the small problems can easy turn into nightmares.


It can be a daunting task trying to find the best deal and value for money so why not give us a call at Total Caravan Care and we can accompany you and give advice on buying the right caravan for you. We should be able to identify if the caravan you intend purchasing has been cared for and regularly serviced and very importantly check for damp ingress. Why not give us a call?

MiRO (Mass in Running Order)

– This is the caravan’s weight with all factory fitted equipment, when it leaves the factory. MiRO replaces the old terms ‘ex works weight’ and ‘unladen weight’.

MTPLM (Maximum Technically Permissible Laden Mass)

– The maximum weight that the caravan chassis can take, as stated by the manufacturer of the chassis. It replaces Gross Vehicle Weight.

Payload

– The weight of items you could load into your caravan. It is derived by subtracting the caravan’s MiRO from its MTPLM.

Nosewight

– This is the weight applied to the towball by a caravan. It is important that the maximum noseweight is not exceeded. Both the car and tha caravan have maximum noseweight limits. The lower of the two is the legal maximum.

GTW (Gross Train Weight)

– The maximum combined weight of a car and trailer combination.

Towing limit

– The maximum weight of a trailer that a car may legally tow. It is often higher than the kerbweight.

Kerbweight

– As defined by EU Directive 95/48/EC. The vehicle’s weight with its fuel tank 90% full, all necessary fluids, driver and luggage of 75KG.