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Dipped / Main Beam Feed

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I'm installing a SatNav system that has the ability to change the display colours for night time viewing. This is achieved by connecting a specific connection on the SatNav system to ground.

I'd like to wire up the system so that the night view is switched on with either dipped or main beam, but not with side lights.

I've setup a relay to switch the SatNav connector to ground on a +12v feed, I'm now looking for the best way to hook up the dipped and main beam feeds from the cars wiring loom.

Is there a single lead that I could tap into for both dipped and main beams, or should I connect up a second relay, given that I don't want to end up connecting the dipped and main beam feeds together?

Also does anyone have a wiring schematic for the dashboard light switch?

Thanks in advance.


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Okay, I spent the last couple of hours removing the drivers air vent and light switch to see if I could get the lights on feed I was looking for.

Once the air vent and light switch was removed, I used a multi-meter and a very fine needle to check out the various feeds from the back of the light switch.

Why a fine needle? Well you can use this to tap into a wire for testing without the risk of creating a short circuit afterwards. Just carefully push the needle into the wire, just enough so it goes through the plastic shielding and makes contact with the wire inside. Then it's just a case of connecting the negative probe of the multi-meter to earth and touching the other probe to the needle. You need to check the needle you are using is a conductor first of course.

I got lucky using this method and the second cable I checked coming out of the back of the light switch was the one I needed. This cable is white with a black stripe and goes to +12v on dipped or main beam.

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Sorry, I couldn't get this reply out to you earlier, but there is a quicker solution for what you needed. Since your low beams are illuminated when your high beams are illuminated (ignition switch on), you just need to monitor the low beams with your relay. That can be done by installing a fuse tap into the output side (upper contact) of either fuse A9 or A10 on your forward fuse panel, underneath the cover. The WT/BK wire feeds both those fuses. Glad to see you found access to the wire by other means, though!

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