Wiring diagram

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Posts: 63
Joined: Tue Oct 21, 2008 10:45 pm

Wiring diagram

Post by achandler » Sun Oct 30, 2011 2:51 am

Can anyone help with a wiring diagram, freehand from an knowledgeable person would be quite sufficient, to enable me to fit a relay to the fog lamp circuit on my 1974 P6B? I have connected the two Square Eight lamps with the correct grade wire to the centre lighting switch on the dashboard, and it all works well, but I have been advised that these lamps pull a fair amount of current and it would be safer to fit a relay.
Unfortunately I have no diagram and have no idea what grade or type of relay to fit.
Any help out there?


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paul williams
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Location: Telford,Shropshire

Re: Wiring diagram

Post by paul williams » Sun Oct 30, 2011 1:05 pm

Hi Adrian,
the following may help.


The relay may have more contacts depending on the one you have/get. When you choose the relay just make sure it is capable of switching the current for the lights. The relay needs to be a 12v type for the coil actuation and typically able of switching approx 10 Amps ( guessing here ) actual current switched is the total power of the fogs divided by 12 which gives the amps taken. Probably best to get an automotive relay from a scrapper, especially one that mounts directly rather than the newer plugin type that need a separate holder. P4 horn relay is a suitable candidate. Mount the relay so as to minimise the length of cables for the fog light power, the length of the coil side is unimportant as it is low current. The relay will be marked with C, NO, NC connections as well as the coil connections. As the diagram shows you need the C Common and NO or N/O Normally open contacts in series with the power feed to the lights. The relay can be tested before installation with a 12v battery across the coil and a simple multimeter set on resistance to check the contacts. You can also take the 12V feed for the switch from the hot side of the headlights if you wish so the Fogs can only be operated when the headlights are on.

This would be suitable and available in NZ, you would have to make your own spade type connections, normally crimped but I would advise if you can to solder them.
http://www.voltelectronics.co.nz/hardwa ... relay.html

Hope that helps


Paul Williams
1929 2 litre Coachbuilt Saloon
1951 Rover Cyclops
1958 Rover P4 90 Monte-Carlo Rally Car
1998 Discovery 300Tdi 3dr
1994 Rover 620 Sli

Posts: 63
Joined: Tue Oct 21, 2008 10:45 pm

Re: Wiring diagram

Post by achandler » Tue Nov 08, 2011 11:02 am

Thanks Paul, very comprehensive. I should be able to find a P4 horn relay without any difficulty in our Club stores.
Much appreciated.

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