Towbar electrics

[Gazdkw]

I'm none the wiser here....

Just to clarify, I have a 12n socket currently, if I purchase a 13pin socket will all the feeds be there to accommodate a 13pi socket arrangement?

[Ian21401]

Is the need for the 12S socket because your caravan has two 7 pin plugs?
As your car already has a 12N socket there is no need to replace it with a 13 pin socket.
Whilst a 13 pin socket could be fitted to the existing wiring on your car it would not give any advantage as the split charge relay and associated wiring is almost certainly not fitted to your car
If you plug the caravan 12N plug into your existing 12N socket you should still have all your caravan running lights so you would still be legal on the road but the caravan reverse lights ( if fitted) would not work.
The 12S socket and plug were introduced to enable feeds to the caravan domestic circuits (lights etc.), fridge, battery and caravan reverse lights. Simple connections from the car’s wiring to the caravan’s domestic circuits and reverse lights and earth are all that is necessary for those. BUT
A “Split Charge Relay” device is required in the car’s electrical feed which is connected to the caravan fridge and battery supply. The purpose of this is so that when the car’s engine is running, and hence the alternator is charging, there is a current being fed to the caravan’s fridge and onboard battery but when the car’s engine is not running and there is no charge from the alternator then the caravan fridge and battery are disconnected and are not flattening the car’s battery. ( the charge from the car’s alternator is being “split” between the car’s battery and the caravan. This is only live when the current from the car’s alternator activates a “relay” within the device to connect the circuits. Hence the name “split charge relay” )
You could wire the 12s socket so only the caravan’s domestic circuits (pin 4. green ) and reverse lights (pin 1. yellow ) and earth ( pin 3. white) were actually connected leaving the fridge ( pin 6. red) and battery ( pin 2. blue ) with no connection. This would mean that they would not draw power from the car’s battery but they would not be running whilst you were towing. If you do not intend to tow for a long trip and the fridge was properly cold before you set out then it would be OK until you stopped and switched the fridge to EHU or gas when sited. Your caravan battery would not charge either during your travel but would be OK once connected to EHU on site. However, if you were not connecting to EHU then the fridge would have to be run on gas and the caravan battery would eventually go flat.
I hope this helps.

[Gazdkw]

Originally Posted by Ian21401

Is the need for the 12S socket because your caravan has two 7 pin plugs?
As your car already has a 12N socket there is no need to replace it with a 13 pin socket.
Whilst a 13 pin socket could be fitted to the existing wiring on your car it would not give any advantage as the split charge relay and associated wiring is almost certainly not fitted to your car
If you plug the caravan 12N plug into your existing 12N socket you should still have all your caravan running lights so you would still be legal on the road but the caravan reverse lights ( if fitted) would not work.
The 12S socket and plug were introduced to enable feeds to the caravan domestic circuits (lights etc.), fridge, battery and caravan reverse lights. Simple connections from the car’s wiring to the caravan’s domestic circuits and reverse lights and earth are all that is necessary for those. BUT
A “Split Charge Relay” device is required in the car’s electrical feed which is connected to the caravan fridge and battery supply. The purpose of this is so that when the car’s engine is running, and hence the alternator is charging, there is a current being fed to the caravan’s fridge and onboard battery but when the car’s engine is not running and there is no charge from the alternator then the caravan fridge and battery are disconnected and are not flattening the car’s battery. ( the charge from the car’s alternator is being “split” between the car’s battery and the caravan. This is only live when the current from the car’s alternator activates a “relay” within the device to connect the circuits. Hence the name “split charge relay” )
You could wire the 12s socket so only the caravan’s domestic circuits (pin 4. green ) and reverse lights (pin 1. yellow ) and earth ( pin 3. white) were actually connected leaving the fridge ( pin 6. red) and battery ( pin 2. blue ) with no connection. This would mean that they would not draw power from the car’s battery but they would not be running whilst you were towing. If you do not intend to tow for a long trip and the fridge was properly cold before you set out then it would be OK until you stopped and switched the fridge to EHU or gas when sited. Your caravan battery would not charge either during your travel but would be OK once connected to EHU on site. However, if you were not connecting to EHU then the fridge would have to be run on gas and the caravan battery would eventually go flat.
I hope this helps.

Yes makes sense.

I tow a caravan on a semi regular basis. I need the facility to cool the fridge and charge the leisure battery from the car.

I'm not fussed on either a 13pin arrangement or a dual 12s/12n arrangement, I just need those facilities.

If I purchase a kit with a split charge relay (seems available in ebay and the like) will that be feasible to wire up?

[Ian21401]

Does your caravan have one 13 pin plug or two 7 pin plugs?
What car do you have? If it’s one with canbus wiring then I cannot offer much advice re wiring connections and you will need someone with more knowledge than I have.
I installed the tow hitch and wiring ( two 7 pin ) myself on my old 940 with standard wiring but we had to pay a professional to fit hitch and wiring to my daughter’s XC70 which has canbus. She opted for 13 pin but we have been disappointed by it.

[Gazdkw]

No carvan has the dual socket arrangement. Like I said previously, I'm not fussed which option I have I just want to know which option is actually possible

[Ian21401]

Originally Posted by Gazdkw

No carvan has the dual socket arrangement. Like I said previously, I'm not fussed which option I have I just want to know which option is actually possible

It would seem that fitting a split charge relay and a 12S socket would be the simplest way forward, BUT
if your car has a canbus wiring system, unless you have the required knowledge, it would probably be advisable to have it fitted by a professional. If you have an older car with “old fashioned” wiring there are a few “how tos” on this forum.
If your car is the XC70 as in your signature then it will have a canbus system and it is supposed to be possible to simply connect trailer wiring into a fuse box behind the trim of the nearside load area but I do not know enough to advise on that.
Was the 12N fitted when you acquired the car? or
Did someone fit it for you later? If they did then approach them to add the split charge relay and 12S for you as they should know what they have already done.
Investigate the wiring to your existing 12N socket. Is it 7 core or 13 core with some wires not connected?
Trace the wiring back to where it connects into the car’s wiring. Does it go to the nearside load area fuse box or is it pickabacked onto some of the car’s wiring harness?
Your way forward will depend on what you find.

[Tatsfield]

If your car is the XC70 as in your signature then it will have a canbus system and it is supposed to be possible to simply connect trailer wiring into a fuse box behind the trim of the nearside load area

Someone did that to my XC70 before I bought it second hand and subsequently the dealer had to replace the entire fusebox and rewire the tow bar system as the previous installer didn't know what he was doing and ended up trashing the rear screen demister!

[Ian21401]

Upon further reflection:
The towing wiring on my daughter’s XC70 is not Volvo but is a dedicated system supplied by a tow bar fitting specialist firm.
In addition to the connection into the load area fuse box there are two plug in connections to two plugs which are part of the car’s own wiring system and are located under the load area floor adjacent to the nearside wheel arch. The system also included two modules, one of which is a twin relay. I’ll try to provide more better information as soon as I can.

[Gazdkw]

Originally Posted by Ian21401

Upon further reflection:
The towing wiring on my daughter’s XC70 is not Volvo but is a dedicated system supplied by a tow bar fitting specialist firm.
In addition to the connection into the load area fuse box there are two plug in connections to two plugs which are part of the car’s own wiring system and are located under the load area floor adjacent to the nearside wheel arch. The system also included two modules, one of which is a twin relay. I’ll try to provide more better information as soon as I can.

Thankyou. I would appreciate that