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It will depend on your car. You may be able to buy a plug in kit from the dealer.

Alternatively you can purchase kits from Towsure.(www.ukcampsite.co.uk/redirect.asp?redir=http://www.towsure.com -I think)Halfords sell general kits.

You need a relay to frun the fridge, otherwise the car battery wil go flat if the van is left connected to the car with engine off.

You can buy a relay kit which incorporates split charge and fridge relays.

If you do not feel competent to do it yourself, any towbar fitter or auto electrician would be able to do it for you.

This is incorrect, you need more than one wire, the relay needs to sense when the engine is running. When I had a Mitsubishi Outlander, the 12S wiring was quite strange, so I would suggest you buy the proper l200 12S loom from your Mitsubishi dealer. My Outlander took the sensing lead from a plug on the wiper motor. The usual "pictures only instructions" took a bit of following, but otherwise it was quite straightforward. I would not bother asking the dealer for help, my dealer (as most do) outsource the fitting of towbars so they had no knowledge of the wiring for the 12S plug.

The sensing lead should be taken from the alternator so that it only switches power once the engine is running and not when the ignition is turned on as it will do if connected to anything else like the wiper motor. Connecting it to anything which is ignition fed isn't right. If your car battery were to go flat when hitched up you would then be trying to draw full starting current from the leisure battery through the thin sensing wire to the accessory you connected to when you try and crank.

You can do it by running just one wire to the front. It is not incorrect as stated above because you can get 'auto-sensing' relays which only need the main power feed and no sensing wire.

Quote: Originally posted by rich2818 on 08/1/2010

The sensing lead should be taken from the alternator so that it only switches power once the engine is running and not when the ignition is turned on as it will do if connected to anything else like the wiper motor. Connecting it to anything which is ignition fed isn't right. If your car battery were to go flat when hitched up you would then be trying to draw full starting current from the leisure battery through the thin sensing wire to the accessory you connected to when you try and crank.

You can do it by running just one wire to the front. It is not incorrect as stated above because you can get 'auto-sensing' relays which only need the main power feed and no sensing wire.

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Post last edited on 08/01/2010 11:53:00

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One of the functions of the 12s socket is a direct feed from the car battery to the van, so you can use the car battery instead of the van. This needs a live feed of fairly hefty cable via a line fuse.

If a relay is used, I accept that one sense wire is needed, but you still require a live heavy duty feed to supply the relay contacts. The relay generally serves for the fridge and battery charging.   Commonsense dictates that a line fuse is fitted too.

The 12S also supplies reverse lights and the Al-Ko trailor stability device fitted to many recent caravans.

On our Bailey (13  pin plug) you can hear it powering up when you connect. The LED on the A frame also lights up.

( We use a 2 socket to 13 pin adaptor as our dealer gave it to us!)

 A relay is simply a device that uses a light current to switch one or more heavier currents.It is a remote switching device.

For example when you start your car, the ignition switch uses a relaitvely small current to switch a very heavy current ( many amps on a cold day!) .

Wihout a relay the switch itself would have to be of very heavy construction to avoid premature burn out- to say nothing of arcing etc!

I have wired several car towbars in the past, but have to admit to paying for it to be done of late! ( Mainly because we have had company cars- or  as for our new Sorento- where the warranty needs to be considered!)

I think I know a little about electronics- being an ex RAF Avionics tech (24 years working on rather complex and expensive kit!)-who now teaches in a college!

Quote: Originally posted by 664DaveS on 08/1/2010

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I have wired several car towbars in the past, but have to admit to paying for it to be done of late! ( Mainly because we have had company cars- or  as for our new Sorento- where the warranty needs to be considered!)

I think I know a little about electronics- being an ex RAF Avionics tech (24 years working on rather complex and expensive kit!)-who now teaches in a college!

Post last edited on 08/01/2010 20:25:28

Post last edited on 08/01/2010 20:29:09

I always fit my own towbars and the electrics, and I always check with the garage, it does not invalidate the warranty. Indeed when Vauxhall replaced a "Friday" Vectra for me FOC, they fitted a new towbar as part of the replacement package knowing full well I had fitted the original one myself.

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The voltage sensing relay is normaly used now. The relay monitors the voltage and only provides power to the fridge & caravan battery when the voltage is at a level commensurate with the car battery being charged. This usually occurs about 30 seconds after the engine has been started and also for about 30 seconds after the engine has stopped.

Relays with a sensing connection to the alternator used to be used, but have been largely superseded by the voltage sensing type.

Hello,

I hope you don't mind me adding my query to this thread since it does concern relays. I did post it on another electrics thread and then saw that one was a bit cold (07)

I want to fit a towbar on my 02 Ford Focus  Zetech Hatch 1.8 and have identified a kit (Towtrust) and single electrics for a reasonable price.  However, I am unsure as to whether I need to fit a relay, I am only intending using it for towng a medium sized trailor. I think not, but would appreciate  confirmation of this and also if Towtrust is a reasonable make (if one is allowed to quote "preferences" on this forum).

Thankyou,

Thanks,