two triggers on one relay

Hi there. Just wondering if anyone could help me out. I currently have two relays set up in my car doing different things. Relay one powers footwell lights in car triggered by dome light on roof. Relay 2 powers fog lights triggered by fog position on headlight switch. What I was wondering now is can I use the output of relay one to also trigger relay two so that when I unlock my car via remote and dome light comes on it will trigger my fogs to come on?

Anyone got any info on this, it would be greatly appreciated..

It depends on many different factors. I will make some assumptions here.....

I assume that your fog light switch is a (+) and that relay 2's coil is permanently grounded.

I assume your footwell lighting has the (+) side switched meaning it is permanently grounded.

If these assumptions are correct you can take the (+) voltage out of the contacts of Relay 1 and connect it to the coil wire on Relay 2 THROUGH a 1A diode with the stripe closer to the relay. You will need to remove the fog light trigger and run it through a 1A diode as well, again stripe facing relay.

The diodes will prevent backfeeding from one source to the other.

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Kevin Pierson

Thanks for your reply Kevin. Both your assumptions are correct to my knowledge. So your saying both wires that I'm planning to use for triggers of relay two go into it through two seperate diodes? Where would I get these diodes?

Yes, you will need (2) 1A diodes. You can get them at an electronics store like a Radio Shack (or whatever you UK equivalent is). The part number should be something like 1n4001 from memory.

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Kevin Pierson

1n400X  X = any number from and including 1 and 7.

KPierson wrote:

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Yes, you will need (2) 1A diodes. You can get them at an electronics store like a Radio Shack (or whatever you UK equivalent is). The part number should be something like 1n4001 from memory.

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ok i think i got it now. just for talking sakes, what would happen if relay 2 trigger sent a pulse up to the + output of relay 1? (if i didnt use diodes)

Without the diodes installed every time you turn on the fog lights it will send power to your footwell lights.

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Kevin Pierson

Hi. I just got my footwell lights installed using the reverse polarity method. The footwell lights work well but when they go off there is a loud buzz from the relay. The dome lights have switched negative and that's why I used the reverse polarity method to power footwell lights. Is there any way to stoop buzzing relay?

https://www.the12volt.com/installbay/forum_posts.asp?tid=114184&KW=bellsracer

hi there, from reading the previous suggestion i dont know whether to use a capacitor or a reed relay now. i could get either tomorrow so was just wondering what you think would be best. could you please tell me what my best setup would be?

i am an idiot wrote:

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https://www.the12volt.com/installbay/forum_posts.asp?tid=114184&KW=bellsracer

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hi there, from reading the previous suggestion i dont know whether to use a capacitor or a reed relay now. i could get either tomorrow so was just wondering what you think would be best. could you please tell me what my best setup would be?

just looking at caps and diodes. is https://www.maplin.co.uk/1a-schottky-barrier-rectifiers-46408 the right one and https://www.maplin.co.uk/metallised-polyester-film-capacitors-361 1uf version the correct items. im not sure which diode to pick if not correct selection could you please tell me what to get from this site?

How were you triggering the relay before you modified the wiring that is causing the chattering? If you had it set up before to work and the relay didn't chatter I would go back to that and then work from there.

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Kevin Pierson

It was set up using reverse polarity method but it always buzzed. It's now just wired directly for now. I would like to use the reverse polarity method again so I can get a positive output so I can trigger my foglights. It works perfectly but don't want the buzzing noise when the lights are dimming..

KPierson wrote:

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It depends on many different factors. I will make some assumptions here.....

I assume that your fog light switch is a (+) and that relay 2's coil is permanently grounded.

I assume your footwell lighting has the (+) side switched meaning it is permanently grounded.

If these assumptions are correct you can take the (+) voltage out of the contacts of Relay 1 and connect it to the coil wire on Relay 2 THROUGH a 1A diode with the stripe closer to the relay. You will need to remove the fog light trigger and run it through a 1A diode as well, again stripe facing relay.

The diodes will prevent backfeeding from one source to the other.

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I am going to use this method but also use a capacitor to stop the buzzing of relay 1. Could you please tell me what legs of the relay I need to put the capacitor across and could you also tell me were the diodes need to be fitted in relation to relay 1 and relay 2 stating which side the stripe is to. Thanks again for everybody's help..