whelen liberty cruise lights flicker question

billm

Member
Mar 21, 2021
20
texas
i hooked up my cruise lights and when the truck is running they are flickering on and off but all the connections are good and the voltage is constant at 14 1 volts any ideas as what would cause this also i have the lights set on the high level TIA
 

JohnMarcson

Administrator
May 7, 2010
10,971
Northwest Ohio
i hooked up my cruise lights and when the truck is running they are flickering on and off but all the connections are good and the voltage is constant at 14 1 volts any ideas as what would cause this also i have the lights set on the high level TIA
TIA- A transient ischemic attack (TIA) is a temporary period of symptoms similar to those of a stroke. A TIA usually lasts only a few minutes and doesn't cause permanent damage. Often called a ministroke, a TIA may be a warning that a full irreversible stroke is about to occur. A TIA is a medical emergency and should be treated as a stroke until proven otherwise. Even if the symptoms subside emergency medical care should be sought.


See, your bar is having a mini stroke....


Seriously though, depending on how this is wired compared to the power for the bar (ie different sources for bar power and switching) can cause the stutter/flicker.
 

billm

Member
Mar 21, 2021
20
texas
Are they on a dedicated circuit or did you tap into another circuit for power?
i tapped in to the park light circuit off of a marker light in my service body and it is constant 14 volts when the truck is off the cruise lights are steady on and when i start the truck and running that is when they start flickering
 

JohnMarcson

Administrator
May 7, 2010
10,971
Northwest Ohio
i tapped in to the park light circuit off of a marker light in my service body and it is constant 14 volts when the truck is off the cruise lights are steady on and when i start the truck and running that is when they start flickering
LEDs on steady burn are sensitive. You probably have alternator noise/pre-failure. If the battery power makes them work right and the running vehicle causes a flicker then the circuit they are on is "noisy" or "dirty" power. You can either get a filter (usually for radios and medical equipment), fix the alternator, or trip a relay from the marker light source but power it from a "clean" source. But at the end of the day to get to the heart of the matter take a look at the alternator, it likely has a bad component or one getting close. Essentially the inherent AC current that the alternator produces is leaking through. This is all very crude terminology on my part, I am not explaining it exactly right, but essentially the alternator produces AC power that gets converted into DC. When alternator components start to fail or simply operate outside their specs, you see (or hear) the effects in sensitive electronics.

 

firebuff17

Member
Mar 28, 2011
774
CT
What year of vehicle are we talking about?

I had similar issues with my truck (‘14 RAM). Lights were fine when truck was in the ACC. But flickered when truck was running.
When the truck is running the BCM sends out pulsed 12 in an effort to give longer life to the halogen bulbs. But when LED’s were introduced, because of the LED nature as we know, the bulbs showed the pulses. In my case, I had to go into the programming of my BCM and tell it to stop by changing some settings. I then used that signal to power a relay. Without changing the BCM signal, the relay would chatter.
 

billm

Member
Mar 21, 2021
20
texas
What year of vehicle are we talking about?

I had similar issues with my truck (‘14 RAM). Lights were fine when truck was in the ACC. But flickered when truck was running.
When the truck is running the BCM sends out pulsed 12 in an effort to give longer life to the halogen bulbs. But when LED’s were introduced, because of the LED nature as we know, the bulbs showed the pulses. In my case, I had to go into the programming of my BCM and tell it to stop by changing some settings. I then used that signal to power a relay. Without changing the BCM signal, the relay would chatter.
it is a 2020 f350 sd xl package gas engine and the other leds on the bed seem to work okay and no flicker issues
 

JohnMarcson

Administrator
May 7, 2010
10,971
Northwest Ohio
What year of vehicle are we talking about?

I had similar issues with my truck (‘14 RAM). Lights were fine when truck was in the ACC. But flickered when truck was running.
When the truck is running the BCM sends out pulsed 12 in an effort to give longer life to the halogen bulbs. But when LED’s were introduced, because of the LED nature as we know, the bulbs showed the pulses. In my case, I had to go into the programming of my BCM and tell it to stop by changing some settings. I then used that signal to power a relay. Without changing the BCM signal, the relay would chatter.
That is really interesting. I was not aware of a feature like that, but I can imagine that would be the same sort of outcome as dirty power from a bad alternator. No matter what you have sensitive LEDs that are showing the fluctuating nature of the power.

Other LEDs working ok may not be a good indicator of the problem. First see if you have any 12v sources that don't do this while the vehicle is running. Using a relay would be a possible solution and diagnostic. If the relay chatters it is probably being pulsed. If it doesn't it's likely an alternator issue, in my experience dirty alternator power won't be bad enough to chatter an automotive relay.
 
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firebuff17

Member
Mar 28, 2011
774
CT
That is really interesting. I was not aware of a feature like that, but I can imagine that would be the same sort of outcome as dirty power from a bad alternator. No matter what you have sensitive LEDs that are showing the fluctuating nature of the power.
Frustrating to say the least.

If you had access to a monitor (I don’t) you’ll see a square wave ( _|-|_ ) rather than a straight line. I don’t know what the hertz would be but fast enough that the eyes don’t see it.
 
Last edited:

JohnMarcson

Administrator
May 7, 2010
10,971
Northwest Ohio
I would not be surprised if you have the same issue as I did.
John M. does bring up a valid point of dirty alternator and I would investigate this also to rule out/in.
I agree, the equipment for testing one theory is a bit expensive. But if you could see if it was 60hrtz cyclic interference vs. small voltage changes you would have your answer. 60 cycle would be a bad alternator showing it's AC side, and pattern of small voltage changes would be likely be intentional voltage pulses from the vehicle's computer. I am again not an expert in this terminology, but I know that AC show through as "dirty power" is a common radio interference problem. The alternator is probably going to need an expensive oscilloscope. The oscilloscope helps to find the output wave form and determine if it is a classic failure pattern. The voltage micro fluctuations in voltage in a repeating manner by design should actually be able to be picked out on a sensitive multimeter. I also recommend the relay as both a fix and a testing method. Voltage changes could "click" the relay whereas 60 cycle would not. Also what ever testing you can do with the power you tapped from the marker light will be good info. I know marker lights are more and more proprietary and maybe the marker lights are designed for the pulsed voltage.

Please update us on this, I thought "pulsed voltage" was a thing of the past that was abandoned when LEDs took over, I guess maybe not. This would be good info for everyone.
 

ur20v

Member
Feb 3, 2017
571
Northern Virginia
Most modern vehicles use PWM to control all lighting, and different circuits get different programming... and that can vary from vehicle to vehicle depending on the option packages of each. So if you've tapped into a circuit that powers incandescent lighting, the pulse that is generally unnoticeable with standard bulbs becomes annoyingly obvious with LEDs. The LEDs in your bed are on a different channel of the lighting controller (my experience is with European vehicles, most use a lighting controller, don't know how the domestics do it) and it's programmed for LEDs with a much higher switching frequency that we can't see. One trick we use on European cars (that haven't had freely available retained accessory power in two decades thanks to CAN and other network protocols) is to tap into the wiper power and run a relay off that. Most vehicles still have switched power at the wiper, and using it as a relay trigger puts no appreciable additional load on the circuit. Additionally you could put a switch on the ground side of the relay coil for full control while the ignition is "on" or in "accessory" (even in keyless/smartkey vehicles).
 

ur20v

Member
Feb 3, 2017
571
Northern Virginia
AC ripple can be problem, but I don't think you'd see it with such a new vehicle like a 2020. Usually you see AC ripple become a problem when the alternator is at or beyond its expected lifespan, and newer cars being so heavily electronics laden will warn you when the electrical system is acting up, either with a check engine light or some other graphic warning on the cluster or infotainment screen. We've come a long way from the old two watt bulb in the dash keeping sentry over your charging system.
 

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