Hey everyone, I was just pulling the OEM radio out of my 03 civic, and I was matching up the wires in accordance to my female harness. Everything matches perfectly, EXCEPT within the male harness, there is an extra wire that is red. Here is what the male harness diagram looks like:

Radio 12v: white/red

Radio ground: black

Radio Ignition: yellow/red

Radio Illumination: red/black

I'm going to skip labeling the speaker wires, because that's all correct.

All of that is correct, and this red wire is located directly under the red/black wire which is the illumination wire for the radio. Could this red wires function possibly be the illumination ground? If that's the case, then I'll have to ground that wire in order to have my aftermarket radio dim. The corresponding wire on the female harness is orange/white, which is also a second illumination wire, but I don't see why I cant use that as a ground if I need to. Thanks again everyone.

Edited September 29, 201212 yr by Ndnkobra

The factory plug illumination (red/black) is positive and is to be hooked to the positive illumination wire on the aftermarket harness.

Older vehicles have both a illumination (+) and a dimmer (-) so you will find both in some aftermarket harnesses.

If you ground out that illumination wire you will morethan likely blow the fuse connected to your dash lights.

Alright thanks. So I'll just leave that red wire alone and not ground anything out since the red/black wire is already connected straight to the orange illumination wire. I'm guessing that the red/black wire has a constant 12v for illumination, while the red probably has a variability in voltage. I'll stick with the red/black.

Correct, just cap it off so it doesn't accidentally touch anything.