Help installing a new changer on an inifnity system

[Monobrow]

Hello, this is my first attempt at this,

I have a 1999 Mitsubishi Galant LS with an Infinity stereo system. I recently bought a new cd player, it's a JVC by the way, and I have the wiring harness for my car-make and also have connected the colored wires together. My old stereo may have had a cd changer in the trunk at one time, but it's gone now. So anyway...

My question is, in my old system, there were two big black plugs on either side of where I plugged in my old wiring harness (I don't know what they are called but they look like the kind that you would plug into a computer, with pins), and there is no where to plug them in into the back of my new cd changer. We tested the cd changer anyway, without the two big plugs, and it seems that the cd changer gets power and turns on, but there is no sound. In the back of my new cd changer, there are two RCA plugs (I think that is what they are called, similar to the kind on the front of a newer television or in the back of a vcr) so I am thinking I would I need some kind of adaptor to connect the two big black plugs into my new unit. Am I on the right track here? Does anyone know what those two plugs could be for, or is familiar with an infinity sound system? I've looked all over the internet for some sort of diagram, but ah well.

Also, when grounding the player with the black wire from the harness, what do people normally do, and what would be most secure?

I'm not very knowledgable when it comes to electronics or cars, in terms of what to call which part, so sorry if my descriptions are very broad. Thanks for your help.