Rewiring or adding to your homes electrical system is a great way to improve its appearance and functionality. But guessing at whether that socket is wired up right is not a good idea… Think dalmatians and sirens — very bad.
To protect against faulty wiring you can use a circuit analyzer like the CA-300A 3-Wire Circuit Analyzer from Sperry Instruments. It plugs directly into the socket just like any other plug, then once power is supplied to the outlet, yellow and red indicators instantly signal which wire is defective by lighting up in an easy to read pattern. The pattern can be decoded with a chart located on the top of the unit. By looking at which lights are lit up, or not lit up, you can see which wire(s) are faulty and fix them.
The 3-Wire Circuit Analyzer is for use on 110 to 125 VAC circuits only and can be found at your local home and garden center or on the net for around $8.