Does anyone know about this please?
My neighbour had a towbar and electrics fitted to his new Vauxhall Vectra. The parking lights on the caravan are very dim. Upon investigation we found that the rear parking lights on the Vectra operate on only 3.5 volts. The output at the 12N plug is about 3 volts. When the brake pedal is pressed one of the parking light bulbs on each side of the car becomes brighter as it then receives the full 12 volts. The bulbs are not traditional dual filament. In addition there are clicking sounds from a large fuse block at the back, nearside of the car when the 12N plug is inserted into the car socket.
The towing electrics that were fitted were not Vauxhalls own make but an ordinary 12N kit. Obviously my neighbour is going to sort it out with the towbar fitter but it would be interesting to know what's going on.
Thanks in advance.
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I think you have explained it yourself... Vaux use 21W bulbs as combined tail / brake lights. In tail mode they are supplied with 3V, in brake mode 12V. You suggest there are 2 side light bulbs on each side, so it maybe that the others are 5W and running 12V, in which case the feed for the tail lights on the socket would need to be switched to these lights. If they also run on low voltage, then a 3V relay is going to need to be fitted, along with a 12V feed from elsewhere in order to get 12V to the van running lights. Not sure about the clicking noise - could be the indicator repeater, or a relay, but it shouldn't click when the plug is inserted if no lights are on. Does it click all the time or just once?
Richard
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Richard - Thanks for that. All tail light bulbs are 12v/21w. The relay (if it is a relay) does make a soft clicking sound all the time even without the lights on. It stops as soon as the the 12N plug is pulled out.
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Vaux use 21W bulbs as combined tail / brake lights.
Are you sure? On my Vectra, and previous Vauxhall Cavaliers, the brake lights are single filament 21w bulbs, and the rear lights are 5/21w twin filament bulbs. In normal operation the 5w filaments are used, and when the fog lights are switched on the 21w filaments are used. If you look at the rear light cluster on a Vectra, the brake lights are housed in a different part of the cluster to where the rear lights are.
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Dynamic Dave - Absolutely certain! The car is 6 months old and the rear light setup is different to anything I've ever come across. It's apparently connected with a new multiplexing system of wiring. It really is strange and very different. There are 4 tail light bulbs (2 on each side), each with a 12v/21w single filament running on 3 volts to give the required light output. When the brake switch operates an additional voltage is sent to one bulb on each side to give 12 volts so that the brake lights are of the correct intensity. Don't ask me why the change, perhaps some electrical wiz will know the answer!
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The way multiplexing works as i understand (and so could be wrong ,still learning)is similar to a dupline system, were different type signals/frequencies are sent down one wire.
At the receiving end i would expect a receiver/decoder unit, which when it receives the correct signal will probably operate a relay. This in turn will supply the required voltage to the lamp intended.
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Instead of large numbers of cables running all around the car,you have one heavy wire to carry the power and a very light wire to carry a signal to a module to tell it what lights to switch on.Copper wire is very,very expensive.
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Not only is the copper wire expensive it is also heavy and car manufacturers want to rid as much weight as possible from their cars.
What you should find is that the 3V is generated by what is called Pulse Width Modulation (PWM). Basically, the 12V from the car battery is switched on and off rapidly and it is the time that the 12V is on that determines the "average" voltage measured by your meter. In this case (3V) you would find that the voltage is actually at 12V for about 25% of the time (25%PWM). At full brightness it will be 100% PWM.
The message to the lighting clusters may be via a communication link such as CAN (Controller Area Network) and as others have mentioned, you have two heavy 12V supply cables and a pair of light signal cables. Alternatively, it may actually be wired directly back to a control module somewhere under the dash. I worked on a project similar to this latter approach and was a halfway-house between full multiplexed systems and the traditional wiring loom.
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For anyone else if you buy your parts from Towsure or Discount Towing,they can supply all the parts,relays etc to suit your car,not just a standard kit.
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Have you tried fitting 12v/21w bulbs in the caravan or re-wire the tail light wire on the caravan to the fog lights ?
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Thanks to everyone for their comments.
kith - Unfortunately there are the additional lights on the caravan to consider - front, side markers and number plate lights.
My neighbour has now gone on holiday so I don't know what happened when he went back to the tow bar fitter. Will keep people informed when I know as this seems to be a very large can of worms especially as more cars are being fitted with this type of wiring.
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this car uses a system called can-bus,the box in the boot making the clicking noise is called a rear electrical centre,the spare slots in this box are for items such as towbars & rear parking sensors etc.........using the can-bus system.
the rear lights are fed with a duty cycle,thats why you found single element bulbs[do not put twin element bulbs in].
you must use the vauxhall wiring kit & it needs to be programmed to the car.
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I promised to update anyone interested about the Vectra towing electrics.
My neighbour had some additional relays fitted and this cured the problem. However,he checked with the local Vauxhall dealer, who said "Programming the Vectra so that it will accept towing electrics causes nothing but problems; you are far better off getting a towing electric specialist to fit the standard kit plus extra relays"!
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