On a 1999 Chevy truck (assuming a full-size model like a Silverado or Sierra), the windshield wiper motor is typically located
underneath the cowl. The cowl is the area where the windshield meets the hood and dashboard. You'll likely need to remove the cowl cover (usually held on by clips or screws) to access it.
It's usually positioned towards the passenger side of the vehicle, but it's best to consult a repair manual specific to your year and model of Chevy truck to be absolutely sure of its location. A diagram showing the wiper motor location will be incredibly helpful.
