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Fitting a bypass relay for towing.

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bingbonguk   
Sun Jan 31 2010, 12:38pm
Member No: #10920
Joined: Sep 17 2009
Location: Nottinghamshire
Hi
Now i know this has been discussed over the years but after searching i could not find an answer.
If anybody has fitted one to their C4......
1 Where did they take their 12v feed from (does it have to be a permanent live)
2 How did they do it, sorry but just want to get it right.
Can i also just say that my car DOES NOT have ESP.
Thanks for any help

1.6 HDI SX Hatch
BigJohnD   
Mon Feb 01 2010, 04:41am

Member No: #82
Joined: Jan 22 2007
Location: Hoylake
Even though you do not have ESP, I would still recommend the genuine wiring kit.

All your other trailer related warnings &c. will work as they should.
slipshot   
Tue Feb 02 2010, 04:53am
Member No: #11254
Joined: Oct 23 2009
Location: Surrey Hills, Victoria, Australia
I believ my installer took the feed from the 12v socket i the rear of the car. Which is OK, except it means you have no power to the trailer when the ignition is off, including hazard lights. Not the end of the world but I assume he could not find a permanent 12v supply up the back there ...
BigJohnD   
Tue Feb 02 2010, 05:29am

Member No: #82
Joined: Jan 22 2007
Location: Hoylake
slipshot wrote ...
I believ my installer took the feed from the 12v socket i the rear of the car. Which is OK, except it means you have no power to the trailer when the ignition is off, including hazard lights. Not the end of the world but I assume he could not find a permanent 12v supply up the back there ...

You need a better set up than that.
bingbonguk   
Tue Feb 02 2010, 12:31pm
Member No: #10920
Joined: Sep 17 2009
Location: Nottinghamshire
Thanks for the replies, i may be on to something regarding a permanent feed and will of course be back to post details if it works out...should be on thursday.
bingbonguk   
Thu Feb 04 2010, 12:07pm
Member No: #10920
Joined: Sep 17 2009
Location: Nottinghamshire
Ok permanent 12v found in fuse box in car
Using parts of the official citroen wiring harness installation guide...


If your car does not have electric seats you will find this grey plug with big red wire attached taped up towards the top of your fusebox. After testing with a multimeter you should find 0v.


Open up the fusebox under the bonnet and remove the plug on the right as shown above. This is just to ease access and you may leave it and struggle if you wish.



Using snipe nosed pliers partially insert a 20A maxi blade fuse into slot 6 as shown above, you can then push it into place by hand.
Testing the plug again you will find you have 12v, mine shows this with ignition off and after economy mode is active.
I will be putting a 15A blade fuse inline for my relay.
Remember safety first, always disconnect the battery before playing with electrics.
Dave_Retired.   
Fri Feb 05 2010, 08:19am

Member No: #1
Joined: Aug 07 2006
Location: Northumberland
That's very useful to know and now a permanent FAQ, thanks for sharing it.
bingbonguk   
Sat Feb 06 2010, 08:06am
Member No: #10920
Joined: Sep 17 2009
Location: Nottinghamshire
No problem Dave, hope others can find it useful.
slipshot   
Sun Feb 07 2010, 11:11pm
Member No: #11254
Joined: Oct 23 2009
Location: Surrey Hills, Victoria, Australia
BigJohnD wrote ...

slipshot wrote ...
I believ my installer took the feed from the 12v socket i the rear of the car. Which is OK, except it means you have no power to the trailer when the ignition is off, including hazard lights. Not the end of the world but I assume he could not find a permanent 12v supply up the back there ...

You need a better set up than that.


I perhaps should do - but it works for the rare times I tow a trailer, I know the issue if something does happen which is unlikely as I will not need to tow a trailer any distance, and that's all it will be used for.

It's good enough for what I need and I'm well aware of the implications - and I bet hundreds of others have it the same too...
BigJohnD   
Mon Feb 08 2010, 04:07am

Member No: #82
Joined: Jan 22 2007
Location: Hoylake
slipshot wrote ...
I bet hundreds of others have it the same too...

You're right, and that's why I get anxious when I see trailers being towed.

Many a time they're piled high, often with kids in the car, with safety booted into touch on the grounds "I don't do it often, m'lud".
justinht   
Sun Oct 10 2010, 01:44pm
Member No: #15849
Joined: Oct 10 2010
Location: Kent
V.useful on getting the 12v feed, but any clues about the trigger connections on the input side of the bypass relay? I've searched for hours for wiring diagrams or some guidance on which wires do what at the rear end, but to no avail.
I understand with the canbus you can't simply trace back from the bulb as some wires carry multiple signals. Is this correct?

If someone can just give me an idiot guide of how they've connected theirs it would really help ... I'm reluctant to start guessing!
BigJohnD   
Sun Oct 10 2010, 05:39pm

Member No: #82
Joined: Jan 22 2007
Location: Hoylake
Hello, justinht, and welcome to C4Owners.org.

You haven't stated which model of C4 you have, but if it's fitted with ESP, do not fit a by-pass for your towing electrics.

Even if you don't have ESP, fit the correct kit so all your other trailer related warnings &c. will work as they should.

Read this FAQ: - Click Here -
and watch this video: - Click Here -
before you decide to by-pass the car's safety systems.

justinht wrote ...

I understand with the canbus you can't simply trace back from the bulb as some wires carry multiple signals. Is this correct?

There is now a sticker in the boot of new C4s warning against cutting into the wiring in the boot.
justinht   
Mon Oct 11 2010, 01:25pm
Member No: #15849
Joined: Oct 10 2010
Location: Kent
Thanks for the quick reply. Should have mentioned it's a 2006 C4 hatch 1.6 without ESP.

I know there are good reasons for fitting the vehicle specific kit, and if Citroen could see fit to sell it at a price that was not astronomical then I'd consider it, but given that the bypass cost just £19 and the Citroen kit is > £100, there are a lot more reasons not to fit it.

BigJohnD   
Mon Oct 11 2010, 01:39pm

Member No: #82
Joined: Jan 22 2007
Location: Hoylake
From the point of view of this forum, and in my own personal opinion, you're strongly urged not to fit a by-pass system to car with a CANBus.

Otherwise please tell your insurers that you have fitted circuitry not approved by the manufacturers, and against the advice of the manufacturers if you're cutting into wires around the rear lights.

If you choose not to tell them, and in the event of the worst possibly outcome it is declared that the fitting of a "by-pass" system is found to be a contributory factor, £80 will be insignificant.
justinht   
Mon Oct 11 2010, 02:36pm
Member No: #15849
Joined: Oct 10 2010
Location: Kent
I appreciate your comments, and I agree that the ESP/TSP system looks great.
But, I have towed for thousands of miles on many different vehicles without such a system, and never had a problem.

If my car did have the system then there would be absolutely no reason I'd be going for a bypass relay. As I don't have it, I can see no compelling reason why I should be paying over the odds. I'm no engineer, but I have built and run a rally car so equally I'm no car maintenance novice and I simply fail to see how fitting a bypass relay can compromise the safety of a vehicle.

Any guidance that can be offered on the wiring would be appreciated.
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