If there are no switches then you likely don't have them. However you do have Torsen diffs which will "lock" up. Depending on the year you may also have TT4 (traction control).
With a Torsen diff when the traction difference between the wheels on the same axle exceeds the bias ratio (5:1 I think and 4:1 for TT4 vehicles), the slower wheel (ie: the one with traction) receives the torque of the faster wheel multiplied by the bias ratio.
However if one wheel loses traction altogether (ie: is in the air) the diff cannot deliver any power to the wheel with traction, so you apply the brakes to keep the free spinning wheel under control and now get much more torque (based on the bias ratio) to the wheel with traction. This is BTM and key in getting a H1 to do what's supposed to do.
If it's a 99, then it should be TT4, and it should also have TT4 badges on the body someplace, (I can't remember where). As has been said, it's likely BTM, which stands for Brake Throttle Modulation. So you're two foot driving. If you start to spin a tire, you add in enough brake to make the Torsen transfer power to the other wheel.
ARB's still work better than either, from what I have seen.
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