Switch #67 is inside the head assembly (pics below from a BOP i restored about a year ago).
Sorry to be the bearer of bad news but unfortunately it is necessary to remove the assembly to access the switch! The adjustment of this switch is fairly critical for the head to operate correctly.
I have another BOP in my workshop @ the moment that has issues with the head assy to do with this switch (among other probs).. will be starting on it tomorrow.
