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post #3 of (permalink) Old 13th March 2007
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By law, you have to have either an indicator light on the dash or an audible buzzer to show that the trailer indicators are working. The simplest way to do this is to wire the indicator outputs on the trailer through a 'trailer flash' relay. Modern electronic flasher unit shouldn't mind the extra load from the trailer bulbs and should flash at the normal rate.

Some may recommend the use of bypass relays on all lights. Personally I think it's overkill and have no qualms about wiring without, but it's your decision. The only thing I'd bother with is a cut-out for the car's rear fog lights. This can be achieved either with an 8 contact socket and 8 core wire, or by fitting an intelligent 'fog off' relay in the feed.

An alternative would be to buy Renault's official wiring loom for the car, which would offer you the peace of mind that you're definitely not abusing the car's wiring, and should also provide the rear-fog cut-out. The official loom also comes with plugs to match the rear lights, so you don't have to hack into the wiring. Just be sure to check everything works properly, as when I bought the official loom for the Laguna, it wasn't wired correctly and I had to make a couple of modifications to get everything working.

If you do go for bypass relays, then you'll need a 12V permanent live in the boot area that's capable of providing enough current to drive all of the bulbs. To be honest, I doubt you'll find one unless you already plan to run a feed straight from the battery for a 12S (caravan fridge/battery) socket.

If you are wiring up a 12S socket, then invest in an intelligent split-charge relay. This takes most of the work out of the wiring, and means you only need to run a single, permanent live feed to the rear of the car.
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