I have 4 wires going into the box that had a fixture that was controlled by a three way switch. Two are clearly white and black and when I test them I get 120 volts. Two are so old that they both look black. So I took a guess and connected what I thought was the white with the definitely white one coming from the power. When I turned on the switch I had 120 volts coming from the white and black. But when I turned off the switch I had about 3 volts. So I switched the two unknown wires thinking I had connected the black and white together but got the exact same results. 120 volts when switched on and about 3 volts when off. So no matter if I have the hot and hot connected or the hot and neutral connected I sill get about 3 volts when it is switched off. Any idea what my problem is?