ground wire, remote wire, and if you feel like doing an extra wire, run an 8 gauge ground from your battery to the back o your car to help eliminate any ground loops.
go nuts with the multimeter, check voltages.
also, if you are using your head units remote power output, :
1 it may require activation through your stereo (menu function, ect)
2 it may not have enough umph to trip your amps on switch (most remote outs are rated for about 500 mw, some amps may require more than that to turn the remote on)