Head moves all the time during gameplay, from side to side. Let me go out right now, lift the glass n check it out for you. Back in 10 mins.

Update - the configuration for the servo is as follows. The wires that are connecting on the servo plug to the small board on the machine are-
far left wire is red
middle wire is black
far right wire is blue
the plug is plugged into the far left servo plug. (note, the board is upside down when u lift the playfield, so its on the right side with the writing upside down, or left side with the writing not upside down if that makes sense). * mine is a replacement servo i believe. i had several new ones from new radio controlled aircraft spare stuff).