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Independently Operated Fogs

DBLE

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#1
Is there a way to mod the light switch so the fog lights can turn on/off independent of any other lights (i.e. light switch turned off but you can still pull it out and the fog lights turn on)? The closest thread I could find was this one, but there wasn't a definitive outcome. There was another post where someone rewired the fogs to be on constantly as DRLs.

I know you can turn on the parking lights and then turn on the fogs but was wondering if the fogs could ever turn on/off by themselves through the factory switch. On my old '06 Miata, it was a matter of tapping into some wires under the hood. Nothing hard. No clue how it works or would work on our cars, though.

Was just curious. . . .
 


Intuit

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#2
Once you locate and map-out the relay for the fogs, it would be simple to tap-in a secondary switch to apply ground (or 12v depending) to that relay via secondary switch.
https://www.digikey.com/products/en/switches/rocker-switches/195?k=dpst switch
One could easily feel behind the lower part of the dash and drill a hole for the rocker switch.

Are you familiar with relays and how they work? A volt meter could be used to map-out the poles.
 


OP
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DBLE

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Thread Starter #3
Thanks for the reply! Unfortunately, electronics aren’t my forte. [sad] I only knew how to do it on my Miata because someone posted a How-To. [:o]
 


Intuit

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#4
If we don't know something, it simply means that it will take us longer; not that we can't do it.

Relays are very simple switches.
The idea is that you use a low current switch, to activate a high current switch.
This is why you for example, don't have massively thick wires running to your beefed-up stalk/dash switch for the headlights. Instead, they can just use tiny little low current wires; that run back to the relay. The relay is what has the thicker wires running back to it. The relay is built to handle the extra current, as opposed to your stalk/dash switch.

So to explain a basic relay, your basic relay will have an input/output with tiny wires, along with with an input/output with thicker wires.

The input/output with the tiny wires as you've guessed, are from your stalk/dash switch.

The input/output with the thicker wires, is actually what switches the high current device on/off.

When 12v is applied to the tiny wire, that in-turn activates the switch for the thicker wires.

There are many different configurations for relays but the basic principal of operation remains the same.
https://www.bing.com/images/search?...-17&sk=&cvid=B4C86CEA73634E45B801A4739C30F776

Once you locate the relay and pull it, you can replicate the pin configuration on a piece of paper and include the label that is assigned to each pin.

Then you can plug it back in and backprobe the wiring harness with a voltmeter. (Never use the "amp" function if it has one - something will get damaged.) The black probe will remain grounded to someplace, such as an unpainted bolt head. You can activate the dash switch and listen to the relay click. While probed, you can record what pin receives what power and what state the fogs are in; which pin has a thicker versus thinner wire.

Relays are often used to switch the ground side of a high current circuit. (safer) So you may find that the thicker wires don't appear to have "any" power, in which case you'll want to use the continuity tester of that voltmeter.
 


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DBLE

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Thread Starter #5
Thanks for the educational post. Appreciate it. [like]
 


D1JL

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#6
This is a relatively easy MOD.
The Fog Light Relay is negative triggered.
So a switch to ground (-vdc) is all that you need.

Under normal operation, the fog light switch tells the BCM to turn on the fog lights.
This is done by sending a ground signal to the fog light relay (R11) terminal #2.
So this method turns on the fog light relay (R11) in exactly the same manor.

In your case just connect a switch from terminal #2 of R11 and the other side of the switch to ground.

Photo of my fuse block is here:




I set up my FOGs as DRLs so an extra relay is was required.


Dave
 


OP
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Thread Starter #7
Thanks and you were the one I was thinking of when I had mentioned a post I found from someone who turned their fogs into DRLs.
 


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