yes. you need a wiring harness. it plugs into the cars harness. otherwise you have to cut off the cars harness and hard wire it. i highly recommend you get a wiring harness.ok, so i got the dash off the caddilac, and now my wires on my HU don't fit with the ones on the car, is there a certain thing to get to fix this? Is it a wiring harness, and if so, what is the purpose for them?