May have pinched wiring from horn switch when putting handle together.
If your tech knows how to enter menu, have him go to analog test 4. A4 is the lift/lower pot voltage. Leave it in test and remove L/L ****, turn pot to a voltage around 2.35 to 2.45, put **** back on and when he tightens set screws make sure the voltage stays. then retry learn. I always have used voltage not resistance. There has also been an ongoing issue with pot suppliers for as long as I can remember.
Don't go for the manager just yet