Multiple sensors on new peterbilt rears

That switch has nothing to do with diff lock engagement..
The air line in your picture is what engages the diff. Lock.
In the condition it is in now the diff lock could be engaged and the light on the dashboard wouldn’t work.

 

The switch is likely standard on the axle lock with this model diff and not needed with newer EOA switch controls to turn on the indicator. As long as everything functions correctly, the switch and pigtail on the diff will never be used.

 

How would the EOA switch control know that the air servo had stroked and applied the differential lock with no feed back from a sensor?
Does it just sense air pressure in the apply line or does it just read the dash switch position?

 

It has no way of monitoring position of the mechanical device and relies on switch position only. With a pneumatic failure, it would not know. Nice huh.....