I put a new headunit in yesterday, opting to use this thread and the old wiring for the rear speakers.

I re-wired the front speakers because it was easy. The rears, however, are obviously a little more complicated.

I was checking out the sheath feeling for the spliced in grounds. Beneath that bundle I spotted two pairs (green/black and black, red/black and black) of wires that look exactly like the speaker wires that plug into the original headunit. I found these under the console, in the front-right corner, right under the sheath that carries wires to the fader. I was confused why these speaker wires weren't in the sheath with the others.

Additionally, right in this spot the wires were split by a connector, identical to the plugs at the headunit (one flat prong, one round prong, on a round plug). This connector is also found south of the rear speakers. I unplugged the two sides, and tested the prongs with a 9-volt. They made the rear left and right pop, respectively. I pulled the rear speakers to check the color coding, and found that my rears (84 coupe) are wired with red/black, green,black striped wires and black grounds, not solid red and green as the guide here says.

I'm curious why these wires are here, in front of the fader, if they ran to the rear speakers. They did not appear to just feed into the fader, or the sheath. They are four separate wires from the six at the fader. Just in case I tested the connections at the fader with the 9-volt to see if I could make the rear speakers pop, but got nothing with any combination.

I went ahead and used running wire splices to tap into the +/- of the wires that i found, and ran new wiring from here to the new headunit. Viola, seems to work great.

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1984 300CD