Hello there. I have a regular 12v led strip light (not RGB), and since BTT boards doesn’t really have pins to connect it and then control leds from firmware (except RGB or Neopixel slots, but they have 5v, so it’s not what I need), I decided to connect it to some pins that have 12v output and can PWM it. So, first time I tried to use second heater pin to connect it, worked fine, but until main heater turned off. When I starting my printing (or just setting some target temp to extruder) - my led start blinking as fast as main heater has PWM value, when heater has 0% or 100% power my led works fine aswell, but when power value like 10/15/50/80 etc it start blinking. I tried to make a video on my phone to show you, but unfortunatelly it can be seen only by my eyes (lul). I though that it’s exactly heater pins issue, so I moved my led on some free slot for fan (controlled one), and it also works fine until heater start working. So, somehow, heater affects other PWM pins (or something like that). I tried it on SKR 2, SKR Pro and on my current board Octopus, same result on those 3 boards. Idk if it’s klipper issue or hardware, so, maybe someone have any thougs about that?
I’m pretty sure that this is not a firmware topic, in the sense that PWM signals are wrongly controlled and that there is some kind of cross-talk between one PWM and another.
I would rather think that this is attributable to the stability of the power supply or in general the stability of the 12V power rail in these boards.
Whereas heaters would largely be unaffected by such fluctuations the human eye is very sensitive to such fluctuations.
You could try an external MOSFET and an own power supply for the LED stripe.
Yeah, I’m afraid that MOSFET is the only solution in this case 
The default cycle_time for output_pin config sections is 100ms - that may be close to the point that you notice it - and close to the point that minor voltage changes make it more or less noticeable. You might want to try tweaking the cycle_time.
It is also possible you have a voltage or cross-talk issue.
-Kevin