What to do with parking brake output (-)

What do I do with the parking break negative wire pictured here coming from the PAC harness I bought, I tied the parking brake from the stereo head unit into the ground wire, do I do the same with this cable or do I just plug it off?

What do I do with the parking break negative wire pictured here coming from the PAC harness I bought, I tied the parking brake from the stereo head unit into the ground wire, do I do the same with this cable or do I just plug it off?