Check the mast cables all of them one by one , check your brake pedal switch.

when amber light flashes are you sure there is no code the amber light should flash like a flash 2 times fast and say 4times slow this is called boot codes because the problem is happening before the self test. l know you replaced the dash and steering module but is any of the controller also have just the amber light on at the same time as dash also the dash you used was it programed for that truck. my self at onetime had the same problem but it was a loose pin connection at the dash display the one clip on the harness to connect to the dash was broke and was not making a good connection with a pin on back of dash. Check all connections real good.