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Old 05-12-2010
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Bench Testing Fog Light Switch?

I'm trying to test a fog light switch with a small ac/dc power supply (probably 1a or less), to see if I can turn on a simple LED strip.
If I can get the LED strip to come on, I figure I'll be able to add a relay to activate other lights, etc.

I have the wiring diagram (somewhere), but I've went through every combination possible, even changed LED strips (and polarity) and all I've been able to get to come on is the indicator light on the switch.

What the heck am I doing wrong here?

The power supply easily runs the LED strips by themselves, even several strips at once... but I can't get the fog switch to activate the strips.

Does the switch require a relay even for such a light load (electrically) as a LED strip?

Ideas? Suggestions?
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Old 05-12-2010
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...should clarify it's an OEM fog light switch...
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Old 05-12-2010
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With the switch on, there will be continuity from the light blue/black to the black ground.

For all functions to work, this switch needs a relay. That's because the ground is shared by the switch, the "on" indicator and the night illumination. So you can't use it to switch the hot side and still have the lights in the switch work. In the factory installation, when the switch has continuity, it grounds the blue/black which energizes the relay coil and turns on the fogs.
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Old 05-12-2010
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Thanks!
That was it Bob.
Got the relay hooked up to the OEM fog switch & it works even with my little pwr supply.

Only problem now is that the dash illumination bulbs are burned out in the fog, defrost & wiper switch on the Explorer bezel... looks like somebody is gonna be doing another LED mod.

I have some 5mm green LED's, but they're very low output & don't light up the switch at all. I tried a 5mm white super bright (with 500ohm+/- resistor on the neg side) LED and it lights up the switch great, except that it's white.

Is 5mm the standard size of LED used for this mod? The LED was snug I'm probably going to do away with the bulb holder & just solder some cat5 wire to the contacts & run the resistor behind the switch area.

I even tried the defrost switch as a momentary with the relay & it works also. The only issue is that I can't seem to get the orange indicator light to come on with whatever light or LED I have controlled by the switch.
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Old 05-12-2010
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Quote:
Originally Posted by buggman View Post
The only issue is that I can't seem to get the orange indicator light to come on with whatever light or LED I have controlled by the switch.
You have to run a branch hot wire back to the power wire of the "on" LED.
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Old 05-12-2010
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Quote:
Originally Posted by rwenzing View Post
You have to run a branch hot wire back to the power wire of the "on" LED.
I'll give this a shot.

Has anyone done a writeup on changing the bulb to LED in the fog/defrost switches? I've searched & found a few posts for the headlight switch & HVAC controls, but didn't see any for fog switches.

I've started modding mine, but the contacts where the half-turn bulb holder makes electrical contact simply refuses to take solder well. I've scraped the contacts thoroughly & coated them with plenty of flux, but the wires pop off with almost any movement. Could my solder iron not be getting the contact hot enough? I didn't want to create so much heat that I damaged internal components in the switches.
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Old 05-13-2010
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Originally Posted by buggman View Post
Has anyone done a writeup on changing the bulb to LED in the fog/defrost switches?
Here is the foglamp switch conversion. I'm guessing that the defrost switch procedure is similar.
http://www.cardomain.com/ride/296394/6
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Old 06-08-2010
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Digging up my own thread....

Would it be possible to re-wire an OEM fog switch to the OEM fog lights & OEM wiring so they come on with parking lights & high beams or just with the key on?

I found an old thread that describes the 95-97'ish under hood fog light mod.
I'm just wondering if the relays need to be re-wired under the hood or if changing something on the switch itself would work. From the looks of the mod, the under hood relay(s) keep the fogs off except when the low beams are on.
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