I have a multimeter now hehe. It was ONLY the radio wiring connector that I was testing anyway.

About the wiring harness... I'm not the first owner, but the factory stereo was still in the car, and the wiring harness did not look like it had been changed at all. There were no signs at all of any previous installs. There are 2 connectors that have wires taped together, so they seem to both be for stereo, but only one is used, and even the other one that isn't hooked up looks nothing like the diagrams I have seen on Install Doctor.