Why Do My F-450 Turn Signals Stay On Solid When the Engine Is Running?

Updated 09/24/2026 | Published 09/22/2026

Question:

Good morning. We are working on a 2023 ford f450. Its a box truck. No taillights, only trailer lights. I installed our own taillight assembly and used the curt 2 to 3 convertor. Everything works fine when the truck key is on. But when the truck is running, the running lights are on which is fine but the turn signal lights stay on , solid. With key in on position, all lights work normal. am i using the wrong convertor? do you have another type of convertor that would work? Thank you Taso SBCfire

asked by: Taso C

Expert Reply:

Hey Taso, thanks for reaching out. I think the issue is the converter setup, but not because the converter itself is necessarily bad/wrong. Your 2023 F-450 chassis cab comes from Ford with combined stop/turn circuits, and those circuits use PWM (pulse-width modulation) when the truck is configured for incandescent rear lamps.

That also explains why everything acts normally with the key on but changes once the engine is running. I would not keep swapping converters trying to fix it. Since you added your own rear light assemblies, I recommend having a Ford dealer or shop with FDRS configure the truck for LED rear lamps. If your new taillights have separate brake and turn functions, Ford also provides a procedure to configure the left/right circuits as turn-only and use the dedicated CHMSL brake-light feed at the rear of the frame for the stop lights. That gets you a clean factory signal instead of trying to make a basic converter interpret the truck’s PWM output.

What does the truck haul and where does it spend most of its miles?

expert reply by: Jesse M