I had a similar problem with a 10-year-old civic that I purchased. A previous owner had hacked the wiring harness and I was unable to get +12 volts on either the +ACC wire or the constant +12 volt wire.

My solution was to run two new wires from the fusebox under the dash which has several places where you can attach wires using crimp-on type of electrical connectors. Be sure to use an inline fuse on these new wires as I am unsure if these connections are fuse protected.

I hope this helps.

Britt