HELP! Horrible hack job on '88 420SEL

[STORMINORMAN]

Previous owner must have just attached wires until there was sound from 4 speakers! Unfortunately I don't even know which radio system was in the car originally. Fader switch has a total of 8 input wires, BLACK, BLUE, YELLOW, GREEN, BLK/WHITE, BLUE/GRAY, BLK/PURPLE & BLK/GREEN. Don't actually know if the fader was even in play after the hack job!

Pulled radio (JVC KD-GS820) and found a horrible mess. Appears there were a total of 5 (?) factory connectors: 1st one is obviously the antenna. My car has the dash antenna switch, which currently works perfectly, BTW!

2nd one is a black oblong/rectangular(?) plug with a brown wire input at the far left position & a brown wire that connects to the 4th position, then an empty space, then a green wire in the middle, the brown wire from the far left into the 4th position, and two wires on the far right, both brown with a blue stripe, the exiting wire has some kind of square plug attached. I believe this is/was the power input plug on the original radio.

THIS WAS NOT CURRENTLY HOOKED UP TO ANYTHING! But the radio had sound.

The 3rd one is a black sheath with a single blue wire: I'm led to believe this is the antenna.

4th has 4 wires: BROWN, RED/WHITE, BLACK/GRAY & GRAY/BLUE wires coming out of a black sheath.

5th has a total of 5 wires coming out of another black sheath: BLUE, GREEN, BROWN and two BLACK WIRES, one of which has a spade plug and then continues on (before it was hacked off).

I have a new JVC unit to install that has what I would consider to be the "normal" type harness: a total of 13 wires.

A) BLACK = Ground
B) YELLOW = 12v+ constant
C) RED = to an accessory 12v+ terminal
D) BLUE/WHITE = to antenna
E) ORANGE/WHITE = to illumination

then the actual speaker connections,

WHITE (+) & WHITE/BLACK (-) = Left front speaker
GRAY (+) & GRAY/BLACK (-) = Right front speaker
GREEN (+) & GREEN/BLACK (-) = Left rear speaker
PURPLE (+) & PURPLE/BLACK = Right rear speaker

From a day on the SEARCH function I'm pretty sure the single BLUE wire in the black sheath 3rd is the antenna, so = D) BLUE/WHITE to antenna on the JVC.

The RED/WHITE from the 4th should be 12v+ constant = B) YELLOW on the JVC.

BROWN from the 4th should be the GROUND = A) BLACK on the JVC.

This leaves C) RED to an accessory 12v+ & E) ORANGE/WHITE to illumination on the JVC.

Plus the 8 speaker connections.

Any assistance would be greatly appreciated.

p.s. WHY, OH why, couldn't the MB engineers used a little longer wires on the fader & window switches?