Diesel Freak | Performance Harnesses and Apparel for Performance harnesses, apparel, hats and accessories for all who love diesel trucks and performance diesel tuning. We ship worldwide! Check our tour schedule to see if we are at an upcoming diesel THE FREAKS · Harnesses · Contact Us · Diesel Freak Dealer · General · Apparel CAT Adjustable Power Harness - Diesel Freak The adjustable set up gives you the ability to control fuel rate at your fingertips. They have been built and tested by a CAT master mechanic. They were developed and tested for two years before being sold to the public. Many have imitated but never duplicated the Diesel Freak brand of caterpillar power harnesses.