NHTSA Complaint #11587342 — 2021 FORD F-250

My F250 was in service for fuel system replacement and to fix both side mirrors which wouldn’t go down after going up. Shortly afterwards I noticed the rapid turn signal you get when tail lights are out. This happened while using a trailer. The trucks rear lights weren’t working at all but trailer lights were. Also was getting the blinds spot and cross traffic alert faults on instrument panel. Dropped off for service. They found a loose trailer plug and reset some things and got it all working again. Soon after the blinkers would flash fast again meaning lights were out, but would quickly stop and back to normal. Later they stayed blinking fast and tail lights out again after stopping starting several times. I tried plugging in my trailer wire harness and it tail lights started working again on truck?? 2 days later Im using trailer again, truck tail lights quit working and getting blind spot and cross traffic fault alerts again!! Still not working after 3 days. had my trailer lights tested where i bought it, they used a battery powered tester found no fault and trailer lights all worked correctly no shorts in system. During times when faults occurred both my enclosed trailer and my rv back up lights would stay on constantly even when not in reverse! Trailers turn signal, brake and tail lights worked but not truck tail lights. No back up no brakes or signal. Just the license plate lights. WHY IS IT EVEN LEGAL TO BUILD A VEHICLE WHERE YOU LOSE USE OF TAIL LIGHTS IF YOUR OPTIONAL FEATURES LIKE BLIND SPOT AND CROSS TRAFFIC MALFUNCTION and CAN RENDER SAFETY LIGHTS USELESS??!! Dropping off at Ford dealer asap to hopefully fix problem. I’ve heard of other trucks having similar problems