Car is an 89 245 with a stock radio

Last time I looked behind my radio (Volvo stock), I saw that there was a bundle of wires connected to the back of the unit. However, there was this black circle thing that looks like something plugs into it, but only that nothing was plugged into it. I looked at my 83 245's amp under the passenger-side dash and see that it has a similar plug with a cord attached to it. I'm assuming that the other end attaches to the radio unit. I'm then thinking that on my 89, the radio side is disconnected. I'm going to take the glove box out and see if there is an amp with a similar plug. So, I'm thinking that to make the radio work, this plug needs to be connected by a cord that also connects to the amp? And about the speaker wires. There are four severed silver wires, which I think are the speaker wires. Do they connect directly to the amp?