1 12 S Pin Burn Out Is There A Cure ?
2 My Car Has 13 Pin Socket & My Caravan Has Two 7 Pin Plugs What Can I Do ?
3 What Height Should My Towball Be ?
4 How Do I Measure A Wheel Rim ?
5. Can I just turn up and get a towbar fitted today?
6. Will my car need a bumper cut?
7. What is the advantage of a vehicle specific wiring kit and do I need one?
8. Will the towbar from my old car fit my new car?
9. My car has parking sensors; will this affect my choice of towbar?
10. Why do towbar prices vary so much?
11. How To Understand Towing Weights?
Question 1- 12 S Pin Burn Out Is There A cure ?
What Is The Problem?
Up to October 1997 and the introduction of new wiring standards for caravans and leisure vehicles, all the 12S system (with the exception of pin 1, yellow, reverse) relied on one heavy wire (pin 3, white) for the earth return. Pins 5 (brown) and 7 (black) were unused. Since EN1648-1, the central pin 7 (black) has been allocated as the refrigerator earth return and pin 2 (blue) is now redundant (previously battery charging circuit). These changes roughly coincide with the introduction of new larger fridge/freezers which, naturally, draw more current.
Pin 7 is an extended male segmented pin in the plug and acts as the æleadÆ to guide the plug into the socket. As such, it is the one pin most likely to suffer damage in use. This, coupled with the higher current draw and the smaller cross sectional area of the wire is causing voltage drop, higher resistance, heat build up and consequently, melting plugs and/or sockets.
You could change your double socket system on car and caravan to one of three continental 13 pin plug systems (either Jaeger or Feder/West Multicon). This, however, would entail changing other caravans and trailers that you may want to tow (though the Feder/West Multicon sockets will accept a standard 12N plug in the centre),and would prove expensive.
Alternatively, you could do a minor modification to the caravan 12S plug wiring. As pin 5 is unused, it is possible to link pin 7 to pin 5 and (provided the brown wire is earthed in the towing vehicle) share the load between both. Additionally, as pin 2 is now unused (though still probably connected to the split charge relay) the same can be done with the feed by linking pin 6 to pin 2.
The advantages are obvious. The combination of 2 cores gives a greater CSA than called for in the legislation and the load (feed and return) is shared by 4 pins instead of two. There will be less voltage drop, less resistance and less heat build up. It is a relatively simple DIY alteration and is inexpensive.
Question 2 - My vehicle has a 13 pin socket but my caravan has two 7 pin plugs. What can I do ?
A converter lead will convert 13 pin to two7 pin plugs, which will work fine on post 1999 caravans. Pre 1999 caravans need modifications. Reason is a 13 pin socket has 1 permanent live (pin 9) and only 1 ignition controlled live (pin 10) Post 1999 caravans have a relay (part no:P32) which is activated when pin 10 is live allowing current from pin 9 to charge the caravan's battery. When the car is switched off (pin 10 dead) the relay is de-activated and pin 9 becomes a supply for the caravan interior lights. Without this relay pin 9 will only provide power for the interior lights. Pin 10 will only provide power for the fridge. Solutions Either fit a relay to the caravan (we fit for ú88.13) or on the conversion lead bridge pin 6 (fridge) to pin 2 (battery) on the 12S socket (this modification if the current is to high may cause overheating)
Question 3 - What Is The Correct Height For My Towball
From the Caravan clubs handbook page 640 (1999 / 2000 edition ) it says the coupling ball is 50 mm diameter and when measured from ground to ball centre should be between 350 and 420 mm (vehicle fully laden - but not with caravan attached) in accordance with BS AU 113c or ISO 1103.
Question 4- How Do I Measure A Wheel Rim ?
The 'pcd'(pitch circle diameter) is the measurement you will always be asked for when enquiring about a wheel rim.
3 stud rim
Measure C, this is the distance from the centre of a stud to the edge of the hub centre. Measure D, this is the hub centre
diameter. pcd=(C x 2) + D
4 stud rim
Measure across the centre hub
from the centre of one stud to
another, this is the 'pcd'
5 stud rim
Measure C, this is the distance from the centre of a stud to the edge of the hub centre. Measure D, this is the hub centre diameter.
pcd=(C x 2) +D
The other measurements needed will be:-
1) The wheel rim diameter, this can be obtained from the information on the tyre
eg. 520x 10, 175x13, 650x16, etc...
2) The wheel section, this is normally stamped in thye rim. This a number followed by a lettereg. 4+ J, 5 J, 5+ J etc....
3) The 'offset' is then another factor to consider, if Ais equal to B, it is a centre web rim, if Ais greater than B, the rim has an offset.
Question 5- Can I just turn up and get a towbar fitted today?
Due to the complexity of most vehicles and customer’s requirements we advise that you phone and book an appointment. Occasionally we can fit a towbar without an appointment but it’s always best to phone in advance
Question 6- Will my car need a bumper cut?
With today’s modern vehicles the bumper very often continues right underneath the vehicle, and this could require an cut to be made in the lower edge of the bumper to allow the towbar to protrude through. Where possible we choose a towbar with the least amount of bumper to be removed. Not all vehicles require a bumper cut but it is advisable to ask if this is of some concern to you.
Question 7- What is the advantage of a vehicle specific wiring kit and do I need one?
Many modern vehicles have incorporated in their electronic systems safety functions such as Trailer Stability Program which can only be activated by using a dedicated wiring kit. Bypass relays, which will allow the lights to function, do not speak to the vehicle computer and are therefore not able to be read by diagnostic equipment. Another advantage is that on some cars the on-board computer can detect when the car is towing and will therefore deactivate the rear sensors.
Question 8 - Will the towbar from my old car fit my new car?
Every towbar is designed specifically for the vehicle so a model change frequently requires that a new towbar is fitted. If the new car is the same model and shape as your old one you can fit the old towbar, but it is best to check with us it will fit. However it is useful to reclaim items such as bike carrier brackets, stabiliser brackets and stabiliser towballs, as these items can often be refitted.
Question 9 - My car has parking sensors will this affect my choice of towbar?
If a vehicle has parking sensors we usually recommend that a detachable towbar is fitted. This is because a fixed towbar could be detected by the sensors when the car is put into reverse.
Question 10 - Why do towbar prices vary so much?
This will depend on a number of factors; whether you want a fixed or detachable towbar, whether you require single or twin electrics, or a 13 pin socket arrangement, whether your vehicle requires a vehicle specific wiring kit and if the caravan you are towing has an ALKO stabiliser which requires a specialised towball to be fitted.
Tel: 01903 854770