GMRS Interference from rear brake/turn lights [SOLVED]

[GotMojo]

I've narrowed down the source of the intermittent interference I'm hearing on my radio. I get a buzzing on all channels whenever the brake or turn signals are active. The noise went away when I disconnected the rear lights (and only the rear lights) but I have no idea what could be causing it. The bulbs are stock -- and presumably incandescent.

This is what it sounds like:

I've checked with another radio and the antenna is ok -- it's definitely coming through the power lines. I am wired directly into the fuse box on one of the unused locations. Ground is good. Radio is a Midland 275.

Does anyone have any idea what the ultimate source of this interference might be? It's almost as if the bulbs are actually LEDs and they have noisy voltage regulators. I may pull one out tomorrow to check and maybe hook up the scope to it and see if there's some sort of PWM activity coming from whatever controls the circuit.

Some photos for the voyeurs:

GMRS radio is under the center console. Mic plugs into pass through next to CB. Doesn't get much more stealth than that!

The CB is on a quick release mount and will only be in situ for long road trips. It also lacks a remote power switch so it can't be squirreled away. President Bill 2.

This is what you have to do to make things look good. There is enough space under the console to hang the sliding mount with 3M tape. All wiring is hidden away.

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[The Real Maverick]

Here's a thought... to reduce the number of wires in ever more complex systems, they often send DATA and power over the same copper wire.

Some crooks learned they could unlock the doors, and actually start the car from a headlamp bulb since it was on the CANBUS data network.

I think it happened in Kias or Hyundais.

 

[GotMojo]

Here's a thought... to reduce the number of wires in ever more complex systems, they often send DATA and power over the same copper wire.

This has nothing to do with the brake lights and turn signals, at least on the Maverick. There's no communication between the controller and the bulb. It's strictly a load sense interface. You can't drop a bulb on a CANBUS differential pair and 'talk' to it.

Point me to source if this isn't the case somehow please.

 

[GotMojo]

After a little digging, I found that the rear lights are indeed being driven by a PWM signal from the BCM and not old school solid 12V.

This thread goes into detail for Broncos.

Edit: The mechanism appears to be programmable via forscan.

 

[The Real Maverick]

This has nothing to do with the brake lights and turn signals, at least on the Maverick. There's no communication between the controller and the bulb. It's strictly a load sense interface. You can't drop a bulb on a CANBUS differential pair and 'talk' to it.

Point me to source if this isn't the case somehow please.

"Called a CAN injector, the device bypasses a car’s security systems and allows thieves to unlock it and start it."

"
There’s nothing special about headlight wires. They’re just easy to reach and networked into the car’s systems.

Modern cars are highly networked devices. Even the simplest, least-expensive new car can contain hundreds of microchips communicating with one another. They also communicate with their own keys — smart keys and key fobs that allow us to unlock (and sometimes start) our cars remotely.

Even headlights today are complex devices. They contain self-leveling systems and can turn their beams with the steering wheel. European law allows automakers to sell smart headlights that can adapt their beams to avoid blinding oncoming traffic.

To power it all, the headlights communicate with other control units in the car. That makes them an easy route for thieves to tap into the car’s controls."

 

[GotMojo]

"Called a CAN injector, the device bypasses a car’s security systems and allows thieves to unlock it and start it."

There is no CANBUS signal to the tail lights!

 

[GotMojo]

Dude, I am not looking to steal a car.

I work with electronics and digital circuits every day. I am very familiar with the CAN protocol. This has nothing to do with it. Your insistence that it does tells me all I need to know about your lack of insight on this matter.

I have narrowed it down to a very specific source already and will likely figure it out on my own eventually. I am here to see if anyone else has encountered this or something similar and has (hopefully) come up with a solution and save me some extra work.

...and documenting it for posterity, of course.

 

[Tbone289]

...and documenting it for posterity, of course.

Much appreciated. If you can scope it, I'd be interested to know the frequency. I'm sensitive to PWM controlled LED lighting and don't notice any with my LED modules, so the frequency must be relatively high.

What product are you using for your antenna mounts? They integrate into the cargo/third brake light nicely!

 

[BlueSpec1]

Could try a clip-on ferrite on the GMRS's 12V wire.
Clip-on Ferrite Ring Cores EMI RFI Signal Noise Filter Noise Suppressor

 

[not null]

If there was a low quality ground somewhere, how would that present?

 

[The Real Maverick]

Dude, I am not looking to steal a car.

I work with electronics and digital circuits every day. I am very familiar with the CAN protocol. This has nothing to do with it. Your insistence that it does tells me all I need to know about your lack of insight on this matter.

I have narrowed it down to a very specific source already and will likely figure it out on my own eventually. I am here to see if anyone else has encountered this or something similar and has (hopefully) come up with a solution and save me some extra work.

...and documenting it for posterity, of course.

Your attitude tells me all I need to know.
Only bad mojo here.
Congratulations. You've made the ignore list.

 

[GotMojo]

Could try a clip-on ferrite on the GMRS's 12V wire.

Already one with a cheap set from Amazon. I put them on both ends of the power wire, the mic wire AND at all the lights. They may have helped a little but did not resolve the issue.

 

[GotMojo]

If there was a low quality ground somewhere, how would that present?

It's certainly possible. I tried two different locations with the same result. Currently it's bonded to one of the bolts just below the fuse box. I also tried a bolt on the center console assembly that's bare metal. Continuity checked out at both locations. I'm still considering getting some star washers to get a better bite into the metal to see if that helps.

 

[GotMojo]

What product are you using for your antenna mounts? They integrate into the cargo/third brake light nicely!

Bullet Point Diesel. Prepare for sticker shock. But hey, free shipping!

I have a moonroof so drilling some holes in the roof was going to be a hassle. This was the next best alternative. Yeah it kind of screws up the ground planes but it's good enough for a couple of miles which is realistically all I will care about. The other end will probably be just an HT with a dinky antenna half the time.

I'm going to dig out the scope today and get some traces now that I know it's not something exotic.

 

[GotMojo]

Congratulations. You've made the ignore list.

Good. Go away.

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