A subsidiary nervous system and processors that bypass your conscious control. Hardwiring is very focused, and applies only to a single skill. Only physical Skills like Guns, Martial Arts, Drive, and Gunnery can be hardwired. The skill is chosen when the Schtick is bought.
You cannot use Schticks or Paths with Hardwired skills unless the GM allows you to bye ChiWires - which depends on the setting but is highly unusual.
If you use hardwiring during a fight or other action sequence, you will overstrain your body, who is not really fit and exercised to perform these maneouvers. At the end of each sequence, you will take a number of WoundPoints equal to the difference between your normal skill (or default attribute) and the hardwiring-enhanced skill value.
Under these limitations, this allows you to use a hardwired skill at your highest skill value.
Taking Hardwiring several times counts as separate enhancements, and does not make the cyber easier to spot.