I have my late dad’s 2003 Silverado. I’m looking at the manual. Are you sure you need the motor replaced or just perhaps replace a fuse? According to the manual for the 2003 Silverado, the windshield wiper motor is protected by an internal circuit breaker and a fuse. If the motor overheats due to heavy snow, etc., the wiper will stop until the motor cools. If the overload is caused by some electrical problem and not snow, etc, be sure to get it fixed.
The fuse block access is located on the driver’s side edge of the instrument panel. Pull off the cover to access the fuse block.
To remove the fuses, hold the end of the fuse between your thumb and index finger and pull straight out.
You may have spare fuses located behind the fuse block access door. These can be used to replace a bad fuse. However, make sure it is of the correct amperage.
The picture in the manual shows the underhood fuse block. Looking under the front hood, the underhood fuse block is the box north of the battery. Hope this helps.