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Discussion Starter · #1 ·
So I installed a set of Rigid LED fog lights on my jeep to the factory harness. I read a lot about people having issues with them flickering when they are supposed to be off. No I read all the solutions of using a 6800uF capacitor and buying premade adapters that solve this issue. Also if you don’t run power to the lights from the factory harness you bypass the whole issue.

This write up is meant to stop the whole PWM and CAN bus theories. CAN bus is not run used on power lines for the lights, end of story. CAN bus is a communication protocol just like any other (ex. Serial or USB) but widely used in automotive or industry. It’s used for its ease of application and immunity to corruption.

Second theory of PWM (pulse width modulation), not there I have Oscilloscope screen shots of this to prove it.

Now for some visual to explain: Pictures in thumbs in order



1. Fog light power on no light connected.

Fog light on.gif
2. Fog light power on with LED light connected.
Fog light on load.gif
3. Fog light power off with LED light connected. The voltage is a saw tooth effect between 9V and 7V.
Fog light off with load.gif
4. Now I also have proof of the 6800uF capacitor working. Fog light connected power turned off.
Fog light off 6800uF.gif
Now for my wild theory of what is going on here. Once the switch is turned off the voltage starts to go down, in response the LED driver tries to regulate and starts to draw more current. Since most LED lights have drivers that will accept a range of voltage there will be regulation that will require more current at lower voltage input and lower current at higher voltage. Ohm’s law proved again. Now I’m not sure what the jeep side is doing but it looks like there is regulation on there to. It sees that the current draw is going up and in response to protect the wiring it bumps the voltage up to lower current draw. Now it still tries to turn the output off and the whole cycle repeats. So no PWM and no CAN bus just two things trying to regulate and do what they are designed to do.
Why does the large Capacitor work? It provides constant voltage to the LED when the jeep is turning off its power, this gives it enough time to completely turn the system off and the LED Light turns off once the capacitor is discharged. That’s it nothing more to it.
 

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Crickets. Bet you didn't expect crickets.
 

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Discussion Starter · #3 ·
I guess not, but i figure I'll put it out there for anyone down the line looking for a solution. Either way the whole PWM and CAN bus stuff was making me skeptical, so I had to prove it to my self.
 

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Makes sense.....wordy.... but definitely makes sense. Installing mine in a couple days. I think I might try the miracle capacitor route.
 

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svt2026, this is an excellent investigation. There is this minor issue that is bugging me though. Why would there be a noise in the line you’ve connected to fog lamp when you’ve turned it off. It is important to note here that there is always 12V appearing on one terminal of the fog lamp, what switches is the ground line, a relay connects the other terminal to the ground when you press the button and the fog lamp turns on. This indicates that there is some issue with your relay. Using a capacitor induces a lag in signal, which means that the signal disappears when your fog lamp starts getting some voltage. Hope it helps.
 

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GREAT THREAD!! just installed a set of UNIBOND fog lamps. I don't have a flicker when off issues but when they are on they have this very slight flicker to them. So in theory if i install a 6800uF it should even out the voltage input also and reduce/stop the amount of light flicker i am getting at the fog lamps.
 

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Discussion Starter · #8 ·
svt2026, this is an excellent investigation. There is this minor issue that is bugging me though. Why would there be a noise in the line you’ve connected to fog lamp when you’ve turned it off. It is important to note here that there is always 12V appearing on one terminal of the fog lamp, what switches is the ground line, a relay connects the other terminal to the ground when you press the button and the fog lamp turns on. This indicates that there is some issue with your relay. Using a capacitor induces a lag in signal, which means that the signal disappears when your fog lamp starts getting some voltage. Hope it helps.
The saw tooth trace is right after the switch is turned off. Eventually the light turns off and the saw tooth goes away. This takes 15-20 seconds and the lights flicker while being turned off. I did notice that as they are off they will flicker on once in a great while. Why this happens I don't know. I think the jeep occasionally checks to for current draw to see if there is a bulb out. I have since converted to a relay setup where the factory harness fog light turns on a relay that has direct to battery power. This is little more wiring but works great.
 

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The saw tooth trace is right after the switch is turned off. Eventually the light turns off and the saw tooth goes away. This takes 15-20 seconds and the lights flicker while being turned off. I did notice that as they are off they will flicker on once in a great while. Why this happens I don't know. I think the jeep occasionally checks to for current draw to see if there is a bulb out. I have since converted to a relay setup where the factory harness fog light turns on a relay that has direct to battery power. This is little more wiring but works great.
I tried the relay trick with having the RI LED pods turn on with only the high beams. As long as I had non-LED headlights it worked great, but soon as I got TL LEDs headlights my relay chattered like crazy for the pods, even with the added module for the headlights.

I am thinking of replacing the fogs with the pods. So what I gather is that the foglight power is stable enough to run a relay without chatter? Now the main question, do you have LED headlights. It seems that relay systems using factory wiring works ok until you swap totally over LEDs.

After I see the pulse when power off, I wonder if I just disconnected the stock fogs, I would get warnings. Just thought of something, I will disconnect one of the bulbs and see if I get a code or warning. Out to the parking lot for a test. Thanks again for the info

edit: shoot forgot I rode the Harley to work haha.
 

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Electrical newbie here:
Is there a way to put this capacitor in line without cutting either of the factory connections (jeep side or fog light side)? I'm running the rigid DOT fog lights and did not want to void their warranty if I didn't have to.
 

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Very interesting. I installed raxiom led fog lights to go with myou new jw speaker headlights as they are much cheaper. I wired them directly to the factory fog lights wiring and have not experienced any issues on mine. Very nice writeup with the proper supporting documentation. Will review if mine start giving me similar issues
 

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Nice work... and that's exactly it. If the TIPM sees a current draw outside of the specifications it expects, that's when you have issues.
 

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The saw tooth trace is right after the switch is turned off. Eventually the light turns off and the saw tooth goes away. This takes 15-20 seconds and the lights flicker while being turned off. I did notice that as they are off they will flicker on once in a great while. Why this happens I don't know. I think the jeep occasionally checks to for current draw to see if there is a bulb out. I have since converted to a relay setup where the factory harness fog light turns on a relay that has direct to battery power. This is little more wiring but works great.
I used the same way, but it is not working fine. When the engine is off, it works fine, but after engine starts, the relay clicks like crazy and the fog light flickers all the time... There are 3 wires from the relay supposed to be connected to a switch. One is ground, one is positive for the switch and one is the output of the switch to control the relay. The way I connect them is I connected the positive of fog light harness to the output wire and negative to the ground and leave the positive for the switch open. Maybe I should also leave the ground open and only connect the positive from the stock harness to the output of the switch as that is the wire to control the relay and relay itself already has the ground connected. Trying to solve this issue. I don't want to waste a button of my spod for the fog light, if I can reuse the stock fog light control.
 

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So I installed a set of Rigid LED fog lights on my jeep to the factory harness. I read a lot about people having issues with them flickering when they are supposed to be off. No I read all the solutions of using a 6800uF capacitor and buying premade adapters that solve this issue. Also if you don’t run power to the lights from the factory harness you bypass the whole issue.

This write up is meant to stop the whole PWM and CAN bus theories. CAN bus is not run used on power lines for the lights, end of story. CAN bus is a communication protocol just like any other (ex. Serial or USB) but widely used in automotive or industry. It’s used for its ease of application and immunity to corruption.

Second theory of PWM (pulse width modulation), not there I have Oscilloscope screen shots of this to prove it.

Now for some visual to explain: Pictures in thumbs in order



1. Fog light power on no light connected.

View attachment 1988193
2. Fog light power on with LED light connected.
View attachment 1988201
3. Fog light power off with LED light connected. The voltage is a saw tooth effect between 9V and 7V.
View attachment 1988209
4. Now I also have proof of the 6800uF capacitor working. Fog light connected power turned off.
View attachment 1988217
Now for my wild theory of what is going on here. Once the switch is turned off the voltage starts to go down, in response the LED driver tries to regulate and starts to draw more current. Since most LED lights have drivers that will accept a range of voltage there will be regulation that will require more current at lower voltage input and lower current at higher voltage. Ohm’s law proved again. Now I’m not sure what the jeep side is doing but it looks like there is regulation on there to. It sees that the current draw is going up and in response to protect the wiring it bumps the voltage up to lower current draw. Now it still tries to turn the output off and the whole cycle repeats. So no PWM and no CAN bus just two things trying to regulate and do what they are designed to do.
Why does the large Capacitor work? It provides constant voltage to the LED when the jeep is turning off its power, this gives it enough time to completely turn the system off and the LED Light turns off once the capacitor is discharged. That’s it nothing more to it.
Which 6800UF capacitor did you use? Voltage?
 
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