OEM fog light to LED
 

Hay there!!! So busted my oem foglights during an off road adventure. I found a set of yellow LEDs that I connected direct to oem wiring and they work great.....EXCEPT...they are to bright for normal road use. So I figured hay no prob ... add a dimmer. Pfft ya right. I wired in my own double din radio with back up cams..cargo lights for my cap and a few other electrical mods... but can't figure out for the life of me how to wire this up. Dimmer has + in - in + out - out. If I read wire diagram for truck correct orange tan should be my +out, blue/black would be my +in. And ground in and out I thought was obvious. When I hook it up like this they do work but at very minimal brightness and dimmer does nothing.

LEDs are not "dimmable" unless they are specifically made to be dimmable

Many people find that out after installing an LED light fixture in a house that has a dimmer and find it doesn't work very well, lol
Most newer LED fixtures will be "dimmable" and it will say that in BIG LETTERS on the box, but also may required a different type of dimmer control

12v LEDs for dash lighting are dimmable
12v Fog lights are probably not made to be dimmable, not really a normal function for Fog lights

You could try a 12v PWM Dimmer control
PWM is pulse width modulation, what it does is to cycle power on and off to an LED, so on/off but faster than human eye can see, but we do see the light gets diimmer the longer its off cycle

Never tried this myself so...................read up on it

Or get a lower wattage LED bulb

The style I bought are dimmable. The issue I am having is more a wiring issue. When I connect the dimmer switch inline with the oem switch it doesn't do anything. According to wire schematics for the truck I should be using orange/tan as my feed out and blue/black as my feed in. But I see that the orange/tan is connected off the relay as well. I can disconnect the orange/tan wire from switch completely and the lights still get power. Thinking that the switch came after relay
.... now i am thinking i have it backwards...that the switch comes before the relay. Posted on here hoping someone has done something Ike this before and could tell me where I have to tie dimmer in so I don't have to go digging threw all the wires.

Are you installing the dimmer before or after the relay? If it's before, then the dimmer will be 'driving' the relay and not the LEDs.

As I mentioned above I believe that is exactly what I am doing ... dimmer right at dash switch using switch wires. Guess that is part 1 of what I am asking....is it switch then relay or relay then switch...schematics don't really tell you this....or maybe I can't read them well enough to tell. That leads to part 2....if it's switch relay then lights does anyone know physically where it leaves relay where accessible. And will this work.

Before proceeding any further, I'd 'bench test' the dimmer with the LEDs. Make sure the dimmer will actually drive the LEDs the way you want. If so, then I'd proceed to installing it in the truck.

Yes....already done.

Here's a video of dimmer right at lights. Hopefully can see that they dim.

Ok well guess not. Doesn't seem to want to upload...and yes it's smaller than 20.

You can't hook up a dimmer to Fog Light switch in the cab
That switch just activates the Fog Light Relay in the engine fuse box, so doesn't power the lights at all

You will need to connect dimmer to the Fog light wires at the lights themselves, so between relay and light bulbs

Thanks. That is what I am gathering. Was hoping that it was other way around(relay went to switch then the lights). Running wires is never fun lol. Just disconnected battery so I can lift up fuse box in engine bay so I can find the wires there.

The wires are exposed at the front by the lights, so not sure why you would want to access them under the fuse box, no benefit

There should be a Splice where the 1 wire from the relay splits to 2 wires, 1 for each bulb, find it, trace wires back from the bulbs
Install dimmer wires on that one wire before it splits

Well for anyone else that wants to do this.... found out for the dimmer I HAVE to use (-) of the light itself..... can't just use any ground.which means running wires from fog light to dimmer(which I have dash mounted) and then back to lights again.

So as far as I can see one light runs up one side of the truck....and the other runs up the other side of the truck, both into fire wall as far as I can tell. So I am going to assume they merge somewhere in the dash. But there is also a tonne of straight black wires in these bundles ...so figuring out which one belongs to the fog light is going to be a chore(see my next post)... still in process of chasing wires to see if I can do it right instead of running all new wires.

Lol sorry about all the back and forth....posting as I am doing this. So where the light wires meet the next bundle of wires the passenger side tan/orange goes off under the rad support towards the driverside. But the negative(black) goes off towards the firewall. On drivers side both wires go off toward the fuse block.

Somewhere they will converge, most likely near the 'computer'... the name and location depends on the year. If you can find the Ford factory wiring book that will give you the information you need to find that point in the wiring.

Ya looked at factory wiring in Chilton. Doesn't tell you much and leaves wires out(There is 4 wires going to fog light switch but book only shows 3). And with the one black wire going off in a different direction I would have to make my Splice pretty much at the lights anyway because as I posted earlier for the dimmer to work it HAS to use the negative from the light itself.

I am seriously considering running a dedicated 12 v and ground from battery to the switch(with a fuse block inserted). The switch still has ingition power so lights would turn off with key...and i believe this would bypass the high beam/fog light off scenario. Then run that to the dimmer and out to the lights. All new wires. Or I could just buy factory fog lights install them and be done with it lol. I just like the adjustability of the bright fog lights for when I am off roading.

Fog light 12v wires run to engine fuse box not into the cab at all
Headlight wires do run into the cab, just FYI

Each fog light has its own separate ground wire

Yes i had corrected myself. And that is why I started at fuse/relay block. That dedicated ground is what is causing some of the issue. In order for dimmer to work it has to use those dedicated grounds. As I said above both positive do go to fuse/relay block but the passenger negative goes off towards cab. I am not going to both pulling any more covers off. Just going to run new dedicated wires from rad support to dimmer.

What is the model number of dimmer?

Ford uses PWM voltage control for several solenoids and even DRL
EGR solenoid, IAC Valve, Purge valve of the top of my head are Ground(-) PWM voltage controls
The devices get 12volt with key on, directly
Computer adjusts voltage by pulsing the ground wire

Outside of 12v power and ground for the dimmer itself to work
You should just be connecting both LEDs ground wires to the dimmer and to a ground in the cab, so just 1 wire into the cab from the LED ground wires

Current wiring
Relay(12v)------------------LEDs==================engine bay grounds

New wiring
Relay(12v)------------------LEDs======/-------Dimmer---------cab ground

Ya little more complicated then I want to get I think. The dimmer is a variable 6 Amp 4 post one off Amazon. I tried using common grounds and lights turn on but won't dim. When I run wires from the black wires right at the lights to the dimmer then I can dim them. I have been just running loose wire and testing all sorts of ideas. Dedicated positives and negatives seem to be the only way I can get it to dim. So I have run all 4 wires now from the lights to the dash. Just gotta hook them up.