'85 300SD Lifeless and won't turn over

Wow! Times like these I feel really alone in rural N.W. Indiana!! I went to change the radio (cassette) to a more modern am/fm/cd Blaupunkt Saturday night. Speaker wires were the hangup and I was told I need a floating ground adapter...? I thought each speaker had both wires coming to the radio and I could connect them as such to each corresponding lead from the new radio. The "experts" said I'd fry the radio and wanted to sell me this "floating ground adapter" for $40. I didn't buy it...I re-installed the former Becker original and had to re-splice the brown ground wire as I was all set to splice and connect ASAP.

PROBLEM: This morning I went out to go to church and when I turned the key over NOTHING happened. NOTHING!! Suspecting a bare wire short on the radio, I took it all out this afternoon, had recharged the battery to full charge and made certain there were no visible shorts. NOTHING still. I did see a wire with something like "MONTEKER" on the side of the wire that was connected to nothing. Other than that - I didn't see anything out of the ordinary. The radio/cassette player works fine. The starter did work excellent - no pause, no hesitation, QUICK spins - easy starts. I can hear a glow plug click off now that I'm in the quiet of the country,too, and away from Chicago NOISE. As a school teacher in Chicago, no option - I have to be there! The '84 TDT I have, my only other option, is near mint inside/outside and completely rebuilt underneath the skin except for the engine so I hate to take it out to the forecast winter snow and Chicago SALT on the streets, but I'll clean it up afterward really good and get the '85 SD back on the road again ASAP.
Thanks so very much for any assistance or advice you can suggest.
Close to desperate in Indiana,
Tom Norris