How does one know which spirit is leading them?
You can be lead by the Holy Spirit when reading the KJV no doubt. He will speak to you through it. He will not rage against his own work in another dialect. He will not attempt to thwart salvation by turning men away from the gospel. You should know you are in error if you are lead to tear down the body of Christ and attempt to sew division.
So take a look at the fruits of the KJVO movement.
1) Arrogance
2) divisiveness
3) slander
4) Hypocrisy
5) misapplication of scripture
6) irrational fear
7) control
Not The Holy Spirit