Installing A CD player

[AlcyoneDaze]

Hi again,

I'm attempting to install a Pioneer DEH-2800MP CD player, I have all the trim and stuff removed, all the wires stripped, sorted, and ready to solder, I'm having one problem, and one query.

1 problem - There are two red/black wires, can I just use trial and error to pick the right one to connect? I don't wanna blow anything out, the FAQ even acknowledges there are two same wires...

Left Rear Speaker - Red / Black (to) Green / Black
Dimmer-A* - Red / Black (to) Orange / White

1 query - I amassed a good sized cassette collection in my lifetime, any possible/easy way to keep the cassette deck working with a new headunit? not a big deal, just curious