Western Star Turn Signal Help

Hi everyone, this is probably a simple fix but wanted some opinions as well. Truck is a 2013 Western Star 4900SB. I switched from incandescent to LED turn signals and side marker lights. After doing so everything worked except I had no right turn signal with the headlights or marker lights on. I wired a small incandescent marker light into the right turn circuit in the rear junction box and that fixed it, when the truck is off. It also works with the key in the ON or ACC position but once the engine is running, no right turn with headlights. Everything else, including hazards work fine just not that right turn. I recently replaced the turn signal switch so I'm sure it's not that. I'm pretty sure I need a new relay or to go back to incandescent bulbs but I don't understand why now it only happens when the truck is actually running. Any thoughts/ ideas/ opinions would be welcome and appreciated.