I have a relay that is already plugged in directly into the brown 4-pin harness. I was just wondering if it needed to be bolted into something metal like the cruise control unit for grounding purposes, or if it would ok to just tape it to some existing wires?

 

i just zipped tied the relay to some other wires and it works fine. I believe that metal piece w/ the hole through it on the relay is just there for mounting purposes when connected to the sub-harness to reach the mounting location; not there for grounding.