The 99 Chevy Tracker's front differential actuator isn't located *on* the front differential itself. Instead, it's part of the
front axle disconnect system and is typically found
near the front passenger side axle, closer to the transfer case. It's a relatively small, cylindrical component that you'll likely see connected to some linkage or cable related to the axle.
It's not always easily visible without some disassembly or at least removing some underbody shields. You'll likely need to get underneath the vehicle to locate it. A repair manual or online diagrams specific to a 1999 Chevy Tracker 4WD will help tremendously in pinpointing its precise location.
