82 300SD Radio Woes

[JumpinJehosipha]

A few questions on replacement of a replacement radio installation in an 82 300SD. First off, it's "mostly" working. But...

Biggest problem is blowing the #1 fuse (Dash lights etc) when the lights are turned on. It had this as a problem before the radio was replaced as well, I was hoping the new radio would FIX that since it blew fuses, oddly, only when the antenna was hooked up! (see my suppositions below about why this might be)

So there's the symptoms - now for the questions:

1. In the bundle having the yellow with black tracer (ignition on?) wire, there is also a brown wire. I assume that is a ground. Is this correct?
2. This brown wire is not currently connected to the radio chassis (nor was it on the old radio). But, a different "ground" wire (determined by deduction from the old installation - it might be wrong) is connected to the "ground" wire coming out of the radio - per installation instructions. This other ground (GRAY) is coming out of what looks like an MB plug with a red and a gray wire - the red is the constant-on. On the "inner" side of the plug, it looks like the wire is gray with purple trace, the other is red with white trace. Is it possible this gray wire is the illumination wire??
3. Can I please have 5 minutes alone in a soundproofed room with the veebilfester who installed the old radio and got the wiring all messed up under there?

My supposition:
So, if I am correct in my suspicion that I have the illumination wire hooked to the radio's ground, I'm only getting a real ground whenever I hook up the antenna, so it blows the fuse. That sound right? It fits the symptoms.

Next problem:
The radio I got has RCA outputs to go to a rear amp, so I'm assuming I can hook this up somehow to get the rear speakers to go using the fader and the current rear amps. (fronts only work right now) Is there a wire for power to the rear amps that I have to hook up as well? If so, what is it?

And lastly, where can I find the wire color codes for this model? I looked on my CD and this forum but came up short.

On a more humorous note, my wife inadvertently gave a very Welsh name to what I call The Blue Whale, she called it "Benz the Diesel" Had to share that with somebody!

Anyway, if you can help me make it into "Benz the Radio", I'd be very happy!