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Help with Towbar wiring

Adrianlle

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Oct 4, 2020
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great_britain
I’ve been changing the twin 7 pin Towbar sockets to a 13 pin as that is easier for the various things I connect to the Towbar. All gone fine save for one thing. I no longer have rear fog lamps on truck when I switch them on. But I do have fog lights on the trailer light bar. When I dismantled the 7 pin 12N I found an 8th terminal with 2 grey wires connected to it. The 8th terminal didn’t have a corresponding pin in the plug. It seemed to be connected by a brass strip to the fog light pin. I left out the 2 grey cables when I reassembled. Now wondering whether I should connect them to the fog light pin in the 13 pin. Before I start messing around with a multimeter, anybody have any thoughts? Below is a picture of the old 7 pin 12N - you can see the extra 8th screw terminal and the brass connector. running to the fog light pin. Thanks.
 

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Tractionman

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Hi again Adrian. Those 2 wires are indeed for the rear fogs. That extra terminal and the corresponding brass strip, are for fog light cut out. When towing a trailer(caravan) and you switch on the lights and rear fog lights, that extra terminal will 'switch off' automatically the rear fogs on the towing vehicle, so there is no glare from the red reflection in your mirrors/rear view. As to the 13 pin, I cant help there, as I have all 7 pin stuff on my caravan and trailer. In absence of any more advice re, 13 pin, it will be a case of your meter job to find which of those 2 wires go where.
How's the axle coming along ?
 

Adrianlle

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Thanks Tractionman. I wondered if it was something like that. The 2 grey wires seem to be permanently connected to the fig lamp pin. So my guess is that if nothing is plugged into the socket then positive power flows to the truck fogs. But once something is plugged into the socket then the power instead flows via the socket to the trailer fog and back through the earth pin if the socket. Can’t get my mind around how that happens though. Any Sparks in here have any ideas?
Thanks for asking about the axle Booked in for 12 Jan as Welders v busy.
 

Steve H

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Hi Adrian. When you don't have your trailer plugged in the brass strip connects the feed to the eighth pin which is connected to your truck fog lights. When you plug a trailer plug in the brass strip is lifted off the pin so that the feed goes to your trailer fog light and not your truck lights. If your fog light on your truck are not working it would be a case off connecting the two grey wires together to restore the feed to the lights. If you want the same thing to work on your thirteen pin socket there are bypass relays that will do that for you automatically. HTH
 

Adrianlle

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Oct 4, 2020
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great_britain
Thanks for all the help. Also done some googling now and 2 options. Either a fog bypass relay or a 13+1 Towbar socket. Will go for the latter as wiring already in place for it whereas the bypass relay will involve finding the existing circuit behind the boot trim panel. So ordered one from Amazon. Will report back.
 

Adrianlle

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Sorted now. Replacement socket fromAmazon of a 13+1 socket. The 2 fog lamp wires connect to the +1 and all now working as it should. Thanks for all the help.
 
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Tractionman

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Well done Adrian, and thanks for update. Always good to know someone has succeeded and how.
 
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