i have a 05 f150 and i bought a wiring harness that connects my old radio connecter to my d3. i know you have to move the mute wire to the upper slot, but do i do it on my wiring harness? not quite sure where to move the mute wire. and how do i ground it. thanks for your help

The wire that you move is one harness on the D3, not your harness that you bought. When you move the mute wire, there is only 1 open slot to insert it on the D3, stick it in there and make sure that it clicks in. Once done, ground the mute, parking brake, and the radio ground all together.

how do i ground it? can i just wire nut them together and run a single wire?

i used a wire nut to connect mine but you can use whatever you like (electrical tape, butt connectors, etc...). The radio's ground is already grounded so just ground the mute and the parking brake wires into it.