Ya, just hook the + to the power wire and than the - to any bare metal on the car. If the power wire is working it should give a reading. Might wanna try different spots tho cause sometimes the bare metal might no be dirrectly connected to the chasis.
If you have a short, you more than likely blew a fuse, otherwise you would most likely be smelling some funky burning car material, or have an exploding battery. Check the fuse.
No, having the RCAs and power wire ran on the same side wouldn't affect the power wire. It may affect the signal coming through the RCAs, though.