Painless Performance was probably one of the first larger companies to offer a standalone wiring harness for the 5.9L Cummins. Many don’t know this but their 5.9L harness can also be used on a 6.7L Cummins with a few small modifications. Standalone harnesses are also available for the Duramax from a few companies with one being Pacific Performance Engineering. The Duramax however needs more than just a harness to run outside of its original GM home; it needs special programming, which can be done in multiple ways (for more on these harnesses and the computers needed to control the engines see our Diesel Conversion Builders Guide on page 90). These harnesses came out years after the engines were offered from GM or Cummins, and it’s because of these harnesses that we can slap a Cummins in a Ford, or a Duramax in a boat.