Differential lock inop

[iceman]

I am not exactly sure how other trucks are but on mine, the interaxle diff (which is the one most trucks come with and always the one you lock before any other lockers) will lock one of the front to the opposite corner in the rear.(think of it as and X) As traction allows it will switch, but only two wheels will always spin. So technically one tire on the drivers side should have turned. But, if both of them on your passenger side were spinning it might be a different setup(i think Meritor does it different) in which case if you did engage your switch it should have turned the tires on the other side. Were they both spinning before or after you engaged the diff lock switch?