Hello lepero - I think you may have tried to post your question using all capital letters. WordReference software converts such posts to the strange format of your first post. Posting using excessive use of capital letters is considered rude.
We need to know more, as maxiogee suggests. What kind of device?
An initial guess is that "harness" is a connection to the main wiring of your vehicle (often referred to as a wiring harness) and "cluster" is a connection to something that is specific to this particular device - but that could be completely wrong.