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I am sure towing electrics feature alot so I hope someone may know the answer to this teaser.

I have just fitted a tow bar to my 2007 Zafira and tried to hitch up a trailer I have aquired. All is fine apart from the brake lights on the trailer do not work.

It is something to do with the following problem I will describe but I cant work out how to resolve it.

The 2007 Zafira as a 1 bulb/1filament tail light, when the read lights are on it glows to a certain level, when you apply the brakes more voltage is applied to the buld therefore making it glow more as a brake light.

The trailer has a 1 bulb/2 filament tail light but when the brakes are applied nothing changes in the trailer light.

Any ideas what I could/should do to get the trailer working please.

Thanks in anticipation

Grant

STOP!!! Before you cause damage to your ECU!!!.

Your car uses a modulated power feed which makes a one filament bulb peform the function of two different lamps.

You need to be using a smart bypass relay which will interpret the signal and convert it to power either 2 bulbs or a 2 filament bulb on your caravan/trailer. Also a smart bypass relay should be used without a shadow of a doubt on a vehicle with multiplex/canbus wiring such as yours, as any fault with wiring, overloading, short circuits can cause damage to the ECU, these can be very costly to repair.

You need a device such as this..

http://www.towequipe.co.uk/products/tf2217ukit-full-bypass-relay---protect-your-management-system.html

You can get cheaper this is just an example of one that works with your car, this link below is the company that make them and have wiring instructions.

http://www.rydertowing.co.uk/towbar_relay_details/towbar_by_pass_relays.aspx.

When you fit the relay use a negative from the vehicle chassis in the boot and the positive feed must come from the fusebox or igntition switch, not any wiring for the rear lights or the boot light!! (i've seen this done!!!).

Any doubt and i'll be happy to offer some help if needed on here, e-mail or phone.

Dale

Thanks to you all.

Dale,

The towbar was from Toequippe and yes they did recommonend the bypass relay which they supplied and has been fitted. The guy there did concur with the fact that unles I used it it could damage the Engine Management System ( I presume that is another way of saying ECU)

So I guess  am still confused, might ahve to take it to the experts I think.

Thanks again

On the LHS of my  2008 Zafira there is a fuse box that has a socket at the bottom specifically for connecting towing electrics to.  If you are DIYing, I would get a dedicated electrics kit and just plug into that.  You may then have to tell the car's computer that you have electrics fitted.

I heard of a case of a guy who used high power headlight bulbs and they caused the engine to go into limp mode.....

modern cars are starting to be fitted with body control modules , these sometimes need configuring to tell the system an addition has been made to the system as otherwise it is seen as an overload & can shut the circuit down.