This has come up in the past and I don't recall what the replies were. I just checked my parts catalog and it's a 'sun sensor' for the VXes with full auto A/C. Part # 8-97114-027-0 for about $45.
A Google search shows cars with auto climate control have them and it measures the direction and intensity of the sun's rays and feeds the info to the auto HVAC system.
The Trooper has the sun sensor in the same spot as a VX. The Axiom has it in the center of the dash a good ways back from the base of the windshield.
Mark
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