Stereo snakes nest; what am I missing?

1989 Mustang LX convertible.

The P.O. has already updated the stereo, but some parts have been removed.

I know it has satellite tweeters in the dash, replacement door speakers, and rear quarter speakers. There's a Kenwood head unit in the dash that is in protection mode. Probably because there is some equipment missing from the trunk area.
Looking through the snakes nest of wires, can you tell me how it was probably set up and what components I'm missing?
I know there was a subwoofer, because there's a knob by the console and I can see the remote wire (the one that looks like a phone plug). Was there also an external amp?

In the rear are:
- 4 speaker wires
- Two RCA wires
- the subwoofer remote and two other wires; power and ground, maybe?

I've been told that I might get lucky and, by replacing the missing components, the Kenwood can be reset. Maybe.

What do I need to buy to put the system back together?

I talked to the stereo shop. He said it had a subwoofer and amp(s). He said that if any of the bare wires touched, that could cause the head unit to go into protect mode.
I've already picked up a powered sub, new amp for the rest of the speakers, 3.5" dash and new door speakers (it looks like the speakers are cheap, Walmart Pioneers).
A buddy is helping me work on the rear quarter window motors. As soon as those panels are removed, I'll find out for sure what size speakers are there and grab them, too,

The plan is to replace all the missing parts, upgrade the speakers, and then attempt to reset the head unit. If it won't reset, I'll look into replacing it then.