Hello,
I have a 2026 F-250 with OEM incandescent bulbs and I added a LED light stick to the rear cap.
The issue is when the truck is off the parking, stop and turn signals work correctly on the light stick.
When the truck is running they go nuts,
After looking at the voltage at the tail lights the voltage when running is ranging from 0 to 14.3v @100hz on the scope.
I used a 1000uF/50v electrolytic capacitor between positive and ground of the wire and it clears up the ripple.
Called a ford guy to check it with the Ford scanner and if he changes it to LED in the computer it doesn't change the pulse issue.

A short video is here:
Could it be since the BCM is using a FET to run the lights that's what is causing the issue?
Anyone seen this issue?


Thanks

 

1) What exactly does you light bar do, be specific.
2) Cars since mid 2000s begun using PWM (pulse width modulation). If you are using, for instance a brake light wire in parallel to run another light, you are doing the wiring incorrectly.
PWM does not provide a constant voltage to the load wire but is fluctuating and flickering, so it's a bad idea since 20 years ago to run any tail light wire in parallel to another light. Even using the brake light wire as a trigger wire to trigger a relay and wire the terminal 87 to your add-on light doesn't work as expected because the trigger wire doesn't provide a constant (but fluctuating) voltage. The workaround is to use a relay before the BCM. If your light bar do 3 things, run 3 relays.
I have seen many people wiring aftermarket reverse camera incorrectly because the install instructions were wrong in the first place. They were using the reverse light wire to trigger the camera when the reverse signal is available at the ECU or at the tranny (depends on A/T or M/T).

Using capacitors to compensate the voltage drop might work with unreliability even if it's wired correctly, if not (like without adding diodes along with capacitors), you also can get some Uxxxx code DTCs. Do it the neat and clean way, run the relay before BCM.