I have an outdoor duplex outlet which was not GFCI, nor was it protected by a GFCI outlet indoors. I tried to tone the outlet to find the specific circuit, but could not, so I shut off power at the main. After removing the existing duplex from the receptacle box, it had two pairs of wires. "No problem," I thought, "I'll see which pair is line and which is load."
I turned the power on at the circuit breaker, then tested with a multimeter. The problem is that both pairs are live. Since both are live, how do I properly wire this into a single GFCI?