Okay so I installed a set of LED headlights on my truck around 3 months ago. Shortly after I found out that when I turn my fog lights on it fuzzes my radio. Now before I go forward with this I am very seasoned at wiring everything. After I found out let the radio was being fuzzed by the fog lights I went and bought a resistor to put in the line. So at the time I did not notice that it had ended my fog lights a little actually a lot. So Friday night I decided to do what I've wanted to do for awhile and build my waterproof fuse box for all of my auxiliary fuses. After I was finished wiring everything up that's what I noticed how much that the resistor had dimmed my fog lights so I left a resistor out. So now here's what's got me stumped, I do not want to put the resistor back in the line but I also do not want my radio to fuzz, so how do I fix this problem without giving my fog lights with a resistor? Like I said I'm very well seasoned and wiring but this has me confused.

 

Are you running the fogs through the factory switch and wiring or an aftermarket harness?
My LED fogs are controlled through the OEM switch/wires and i haven't had any issues.
Are your fogs and the radio sharing power and/or ground?

 

I built the harness by hand and I am running 1 fuse per powered wire from the battery, 3 prong lit switch, and a 40 amp relay. When I wired it before before I only had 1 powered wire fused and it still did it before, then I ran a resistor and it stopped the problem but dimmed the Fog lights.

 

Sounds like a ground loop. Find a new spot to ground your lights and see if that works.

 

Both lights are grounded perfectly, in fact I tested the ground spot before I put them there. The relay is also grounded properly, which it wasn't grounded properly before. I am clueless.

 

It has nothing to do with grounding. It's the frequency at which the chips are switching. Only way to eliminate it is to get better LED's that have more robust filtering or go with ferrites. Two or three wraps of each lead it's own ferrite will probably knock it out.

 

Ferrite? Please explain, not sure what that is?

 

This is good bathroom reading.

http://audiosystemsgroup.com/SAC0305Ferrites.pdf

I would get a couple toroidal chokes and see if that knocks it out.

 

I read up on Ferrite chokes last night so I'm up to speed on them. Now my question is do I need to put them on the light wires or radio wires?

 

They need to go on the light wires. The signal is originating there so that is where you want to kill it. You radio is just acting like an antenna and picking it up.

 

Sweet I'm going to go pick some up today....

 

I may be showing my age but back when I was younger most cars had a capacitor on the ground side of any RF noise producing device i.e. alternator, AM radio, CB.

 

Yes.

Put them on both. Block the interference at the transmitter (the lights) and the receiver (your radio).


That would not be a bad idea. Both the ferrites and the capacitor can be used to get rid of interference.

By the way, a torroidal choke does the same thing as a ferrite but is typically used on circuits that draw high power, or where higher levels of interference are expected. Probably not needed in this case.

 

Hats off to both of you and the post who suggested to buy a higher quality light. I have 2 cigar box's full of choke's I've built up over the years mostly salvaged from old radios and amps misc. electronic gear. You never know when one might be needed working on older radios and projects.